The programming instructions for labelling zones on a PK5500 keypad are found in the keypad manual (not the main installation manual). They are a bit vague, so to summarize the sequence would be:

*8
Installer's Code
*
001  (for zone one, 002 for zone 2 and so on, must be 3 digits)
XXXXXXX Label XXXXXXXX  (see below for instructions to change the label)
*
* (save)
Then the next section. 
When done, use ## to exit programming

To change the label, use the arrow keys to move the underline to the character that needs to be changed then use the numbers 1-9 on the keypad to choose the number.  Each time you press the number you change the leter as outlined below.

[1] A,B,C,1[2] D,E,F,2
[3] G,H,I,3
[4] J,K,L,4
[5] M,N,O,5
[6] P,Q,R,6
[7] S,T,U,7
[8] V,W,X,8
[9] Y,Z,9,0