Normally you can follow these given steps..It can be different for different model.....
Turn on the unit, and open the print-carriage access door by lifting the handle until the door locks into place.
The print carriage will move to the center of the unit. After the print carriage stops, release the gray print carriage latch and lift upward to access the printheads.
Remove the old printhead by lifting the printhead handle and pulling upward.
Being careful to touch only the black plastic remove the new printhead from the packaging and gently remove the plastic tape.
Using the printhead handle, push the new printhead firmly down into the appropriate slot; matching the color on the top of the printhead to the color on the printhead carriage.
Move the print carriage latch down, and make sure the loops catch the hooks. Snap the latch into place, and close the print carriage access door.
After the message to align the printheads appears in the front panel display, press Enter . A page prints to confirm alignment.
If you need any kind of technical assistance you can contact support cell at http://www.vtechsquad.com/