U have to pull the radio out. If u can unplug the radio make sure u have the codes to turn it back on. It takes a little two handed pushing from the rear of the climate control to get it out sometimes, mine took a little to get out but it will pop. So all the best to you!
How to remove radio knobs in 2004 1/2 and newer S40
I have actually removed the knobs on my radio and replaced them due to the same problem. Basically, you just grab the knob tightly and pull straight out and it will pop out (including the center section of the knob). You have to pull pretty hard, but I've done it a few times with no issues.