What do I have to do to replace disc break drums

That depends if you have disc or drum breaks on the front? More than likely you have disc breaks on the front. If there disc you can only bleed the system @ each wheel ie ( air in system / low pedal etc.) Drum breaks you can adjust to factory specs!

Was the back brake a disc or a drum? If its a drum u have to adjust it by opening a little hole with a rubber cap behind the brake drum try use of a brake tool if u got alot of extra money to spend or a flat screw driver will do if its a disc most of the time the adjuster is behind the hand brake lever u can tighten the nut that pulls the cable

Try this:

Hi Chery, squeaking from the brakes isn't at all uncommon. The simplest and most likely cause is dust in the braking system. This gets between the fristion material and the disc or drum, heats up and creates the sound. Going beyond that, it might be a lack of lubricant (special grease) bwtween the disc pad (or brake-shoe) and the actuator/s. Worse still it's possible it's indicative of worn out brake friction material in which case it could well be the base of the pad or the brake shoe rubbing against the disc or drum. This last will entail a brake overhaul - fitting replacement pads and/or shoes, and if this has caused disc or drum wear, their repplacement too. Good luck!

this can be a big job u need new master cylinder, proportioning valve, conversion kit (or donor car) for rear hubs, rotors etc. if has anti-lock brake system gets even more complicated

You need to have it taken apart and cleaned. If it has drum breaks in the rear try replacing the shoes and spring hardware kit. If its pad and disc then try replacing the pads and possibly the calipers. Its very common for drum breaks to stick on this vehicle more so if it has sat for any length of time.

drum and disc breaks
drum brakes are the type that have a drum covering the brake shoes
disc brake has a rotor and caliper-they look similar to the front brakes

If it has drum brakes get the drums machined or if it has discs get the discs machined to stop the vibration as with age and heat and water splashes over time the discs and or drums go out of round causing the pads(discs) shoes (drum brakes)to cause a vibration when they are applied,

You do not require a mechanic to do this job. lst remove any wheel front or back. You probably have front disk and drum on the back.
To remove the rotor, you will see two bolts holding brake capalier on the rotor. Remove these and pry the capalier from the rotor. Now you need to remove the pads. Simple to remove, but when replacing you need a 6 inch c clamp to force the pressure mechanism back into the rotor in order to replace the pads. Remove the rotors and have them researfaced any any machine shop. Cost around $10 per rotor. Pick you up some antisizing compound and high temp grease. Follow instructions on the label. Now remove a back wheel, if you do not see a rotor then its a drum. To remove a drum you will need a several tools to replace the drums. Purchase these at Harbor Freight or Sears. Much cheaper at Harbor freight. Now remove the other wheel and repair one wheel at a time, by checking back wsith the wheel that has not been disambled. Before replacing have the drums reserfaced. Now once the job is completed you need to tighten up the wheel by using the special tool which you purchased. Tighten a little at a time AND ONCE THE WHEEL becomes hard to turn back off a turn. Do the same thing to the other wheel. May take you all day to do the job. But it's the way I learned to do a brake job. Hope this is helpful.

If I am correct that truck has rear drum breaks? If this is the case the adjusters sound as if they were not brought in enough for proper clearance between the drums and shoes. If this is it I'd remove the rear drums and adjust for proper clearance (there should be no drag with drum breaks. If they are disk breaks I'd say the calipers are stuck and keeping tight on the discs; if this is the case I'd replace that calipers with new or rebuilt units.
I hope this may have helped,
Tom