Whoa, whoa! Don't pop the chrome thing off. There are little nubs on the back that are staked over. Popping it off will make it harder to get it back on and have it stay on.
If you have the door open, it is easy to get the cylinder out. Put in the key. Looking down from the top, there is a little slit with a gray tab in it. With an improvised tool, press that tab down while easily pulling on the chrome knob from the front. Once the gray tab clears, you should see brass ones. They should clear if you have the key in but you may have to press them down also. Pull the cylinder out and make sure you don't drop it or the brass tabs that set the key pattern will go all over. Wrap it with tape until you need to put it back.
Hope this helps.
Bob