information on replacing rds radio

I have a 2004 Grand Prix that I am having to replace the am/fm radio with 6 cd player/changer in it. I have purchased one off of eBay that came out of a 2007 Grand Prix. All of this stuff I am seeing about having to get the one that I am going to install in the car "unlocked" before it will work has me so confused. I am about to pull my other 3 hairs out. Can someone help me and explain this process to me.

Take it to the dealer,has to be done with the Tech 2.GM did this in 2001 and don't ask me why they did this.There is a number under the spare tire cover which the numbers are shown on the Tech 2.