I have a Simplex Kaba Ilco Unican 1000 keyless lock and I want to change its password. But I don't know how to do it. Could you please help me. Thanks.

I believe you can find this to be relevant:
I found this instruction elsewhere on this site ( thanks to pctuneup191):

PROCEDURES TO CHANGE THE COMBINATION OF

SIMPLEX 1000 SERIES CIPHER LOCKS


1.) ENSURE THE DOOR IS OPEN.


2.) INSERT THE DF-59 CONTROL KEY INTO THE COMBINATION CHANGE PLUG ASSEMBLY (ON THE BACK OF THE DOOR) AND UNSCREW THE CYLINDER BY TURNING THE KEY COUNTERCLOCKWISE.


3.) TAKE THE CHANGE PLUG ASSEMBLY COMPLETELY OUT OF THE DOOR.


4.) TURN THE OUTSIDE DOOR KNOB CLOCKWISE ALL THE WAY UNTIL IT STOPS, THEN RELEASE THE KNOB.


5.) PRESS IN THE EXISTING COMBINATION FIRMLY.


6.) INSERT THE SPANNER WRENCH IN THE COMBINATION CHANGE SLEEVE. IT SHOULD INSERT AT THE NINE O'CLOCK POSITION.


7.) TURN THE SPANNER WRENCH GENTLY CLOCKWISE UNTIL IT STOPS AT THE 12 O'CLOCK POSITION. NOTE THE NOTCHES IN THE COMBINATION CHANGE SLEEVE MOVES AS THE SLEEVE IS MOVED.


8.) TURN THE SPANNER WRENCH COUNTERCLOCKWISE BACK TO THE NINE O'CLOCK POSITION UNTIL IT STOPS. REMOVE THE SPANNER WRENCH.


9.) TURN THE OUTSIDE DOOR KNOB CLOCKWISE (ALL THE WAY, UNTIL IT STOPS), THEN RELEASE.


10.) INSERT THE NEW COMBINATION BY PRESSING IN THE BUTTONS. USE AT LEAST three numbers and a maximum of five.


11.) TURN THE DOOR KNOB CLOCKWISE ONCE, ALL THE WAY, UNTIL IT STOPS. HOLD IN THIS POSITION AND CHECK IF THE LATCH IS RETRACTED.


12.) RELEASE THE DOOR KNOB.


13.) TURN THE DOOR KNOB CLOCKWISE ONE MORE TIME TO THE STOP POSITION. AT THIS POINT, THE LATCH SHOULD NOT RETRACT UNLESS YOU USE THE NEW COMBINATION.


14.) REINSERT THE CYLINDER INTO THE BACK OF THE DOOR BY SCREWING IT IN CLOCKWISE WITH THE DF-59 CONTROL KEY (DO NOT OVERTIGHTEN!)


REMOVE THE KEY.

A Df-59 key can be purchased at this site:

http://absupply.net/kaba-access-control-lock-1000-series-key-df59.aspx

The spanner wrench (SMPBC201278 Simplex:SpannerWrench $9.00) referred to can be purchased from this site:
http://www.ckilock.com/Mpage18.asp

Here is the "literature grid" from the KABA website, which has manuals and parts lists for the Simplex mechanical pushbutton locks:
http://www.kaba-ilco.com/access_control/literature/literature_grid_mechanical_pushbutton_locks.aspx?id=13

Here's the website to continue your search:
http://www.kaba-ilco.com/access_control/products/eplex.aspx?id=6

Good luck!

Good Luck!