I need to change the spark plugs but cant get to the ones in the back

check for good spark ,if ok check fuel pressure and flow, if pressure is low replace fuel pump, if flow is low replace fuel filter and check fuel regulator for leak back.

you can read the FSM
or read the pages on topic
here
alldata.com
diffr. years, may have different engines, diff. size engines (options) too.

you post is non specific, you never said what you cant do.
nor what was hard, or confusing, ?
so cant help.
if you have the engine with COP coils. you remove them.
1 by one, blow out the dirt in the wells.
then remove the spark plug (CCW)
then gap the new plug and put it back at about 20fl/lbs torque max.
if you cant reach a plug, use the 3/8" drive
Universal and extensions. some take 2 exentions.
one for the well and one to lean back.

alldata.com its all there,...
or post stopping point, or show photos of the place that befuddles you.

Well should be pretty basic youll need a 3/8 ratchet and an extension and a spark plug socket, if you cant see the plug wires and plugs you may need to take a cover off but they should be visible at the top of the engine, remove the plug wire and unscrew the spark plug, install new plug and replace the wire, do one at a time so you dont get the wires mixed up

Go back and pull each spark plug wire and put it right back on. There is probably a loose one. This is assuming that you didn't pull all the wires off at once when changing the plugs. If you did, the you put the wires back on in the wrong order. Then, you'll need to find a manual online for the correct wiring order for the plug wires.

If they are on in the right order, you need new plug wires. They don't last forever!

This is a pretty straight forward job though I cant recall if you need to do anything special to reach some of the plugs.
You may need a tool to pull the boot off of the plugs. Now is a good time to go ahead and change the plug wires. If the plug wires stick to the plugs hard enough they could break during removal.
You will need various length of extensions and a special socket for the plugs to help prevent breaking them. Experienced mechanics often do it with a regular deep socket but better safe then sorry.
unplug the wires from the spark plugs makeing sure to keep them in a logical order because they have to go back in the same spot they came out from. If you are worried about messing up here then just do one at a time.
Unhook the spark plug wire from the plug. remove the plug. check the gap(these days I notice that most of the new plugs are already gapped to the right spec. but it doesnt hurt to double check) on the new plug. Carefully thread the new plug in and tighten it up. plug the spark plug wire onto the new plug. Move to the next plug, rinse and repeat.

not to bad you'll need long extension, front one are there in view, the back one's remove spark plug boot (long one) and with extension you can reach spark plug's.

You might have a security problem. Cant see it bein the fuel pump with how new the vehicle is. Not a spark plug problem. Need to check if your getting spark from the ignition coil. If you are then you need to make sure your gettin fuel to the engine.

ok that is not the easy the ones in the front those are the easy ones but the ones in the back thse are dificul ones so in order to change those spark plug you need to race the car and try to change them from underneath this is one way the other way is to remove the intake sistem and change them from the top

The spark plugs are under the 4 spark plug wires.

Here is an image. http://image.turbomagazine.com/f/8851894/0406tur_03z+nissan_altima+engine_bay.jpg

Under the 4 black wires next to the blue oil cap.

Hi Glloyd806

the spark plug gap is .054
This is at best difficult and if not done right can destroy your heads ( about $2700.00). My advice is to have the dealership take the risk. However, If you decide to change the spark plugs yourself you'll need to know a few critical things first.
The 5.4L has aluminium heads, there is a design flaw in that the thread depth is to shallow, only 4 or 5 threads. because of this it is EXTREMELY IMPORTANT to apply anti-sieze on the threads of each spark plug and torque the plugs to NO MORE THAN 14 LBS. Also, if the plugs have been improperly changed before, it is to late, and you will rip the threads out when removing the old plugs.
Still wanting to do it yourself? OK here is how it is done;
Each spark plug has it's own coil, you will need a 8mm socket to remove the retaining bolt. Then disconect the coil wires on the coil. pull out the coil assembly (coil and boot). they may be stuck a little so you may need to wiggle it out. Now you are ready to remove the spark plug. You will need a THIN WALLED 5/8in spark plug socket, at least one extension, and on the #3,4,7, and 8 spark plugs you'll need a universal joint. the holes that the spark plugs are in are machined very thght and I found that I needed to try several different sockets before I found one that would fit inside the hole. Remove the old plug. apply anti-sieze on the threads of the new plug and install. DON'T CROSS THREAD, THERE IS ON SECOND CHANCE! TIP.. replace the old rubber boot with a new one and apply a liberal amount of spark plug moisture protectant gel inside the boot, spark plug end, this will save you from spark plug mis-fire due to moisture in the future. Place the new boot back on the coil and place the coil/boot back into the spark plug hole, it may need some wiggeling. Replace the coil retaining bolt (anti-sieze), reconnect the coil wires. Now do this 7 more times.

In all honesty, take it to a Mechanic, because this is a real pain in the....

Best of luck, and I'm not responsible for any damages you do :(

Lazaruselite