Sometimes it's written in the car's manual or on a slip of paper in the tool kit or glove box. Should be a 4-digit code, IIRC.
If it's not there, you should be able to get the code (for free) from the dealer if you bring in the VIN and/or the ID number on the back of the stereo. You might call the dealer first and see if the VIN alone is sufficient to save you the work of pulling the radio.
If you do have to pull it, all you need is a tiny little allen wrench to loosen the catches on the sides of the radio. A Bentley manual (if you have one) would probably have a picture, or someone else here might have one to post.
Glad to hear you kept the car, and that it's treating you well.
Best of luck,
Robin
Robin
72 Chevy K10
01 E39 M5