I have a 2000 sunfire and want to replace the radio with a radio from a 2001 sunfire, but the theftlock wont let me unlock it, I tried the procedure to unlock the radio but it doesn't work, do I have to change the computer program to allow me to use the radio?

No It should work. What unlock proceeder are you using? If the previous owner if the 01 radio set up the theft lock you need to do the unlock proceeder for the VIN number of the 01 radio.

im using the procedure of pressing the preset keys etc, I think the radio detects its not in the original car

No you need to get the unlock codes to properly unlock the radio. See link

Delco Lock Codes - Unlock Any Locked GM Delco Radio Showing LOC or INOP!

When I worked for the dealer we had a direct line to delco to get the unlock codes, looks like you need to pay to get them now

Sorry, upon further research you will need to take it to a dealer or find someone with a tech 2 to sync the radio to the BCM on a 2000 and newer radio.