Repalcing the ink cartridges

try this link might help you... replace ink cartridge in HP officejet 4215 all in one Google Search

Turn on the HP printer. Lift the printer cartridge door, which is the right side of the printer, revealing the black and color ink cartridges. Push down on the front of the cartridge you need to replace and pull it out slowly. Unwrap the new ink cartridge and peel off the tape. Insert it at an angle into the cartridge slot. Apply gentle pressure until it clicks into place. Close the cartridge door and press "OK" when prompted.
References:

HP User Manuals: HP Officejet 4215
Hope this helps you :)

Either:
* empty ink cartridges
* clogged ink-jets, such that no ink can be sprayed onto the paper

Use the HP software to check the ink-levels in the cartridges.

Run a few "print-head-cleaning" cycles. If still no output, then replace the ink-cartridge(s).

usually when you open [flip up the lid] on a hp there is a big sticker with a drawing of some ink cartridges and numbers in the center of those drawings all you need is those 2 digit numbers for when you go to the store the cartridges have those corresponding numbers on them hope this helps and please vote

HP 27 cartridge is not compatable for this printer. Supported cartridges are :

Back : HP 56
Color : HP 57 , HP 28

Photo cart : HP 58

Just replace the cartridges that are empty. If the other colors are LOW, the printer should tell you when they need to be repalced. Just be sure you keep one extra black and one extra color cartridge close all the time.

your HP Cartridges are not compatible with that kind of HP Printer, buy 56 black and 57 color. It might work...

Are you sure you installed the ink cartridges correctly? They should snap in and then you should be able to do a Printer Test/Align cartridges function. 
Which error message is it putting out? 

Please check :-
Protective tape on a new ink cartridge has been removed. Contacts on the ink cartridge are not meeting the contacts in the carriage correctly.

Then try and do a head clean and printer head alignment.

open the right side of the printer by lifting up. the cartridge holders will come to you. slide them in and lift up to fully install them. put the cover back down and you're ready