How not to brake the glass....

Have just done this on the weekend. A tool like Robj posted would be ideal for the chrome, but I did it with a very fine flat-head screwdriver - lift up the chrome trim from the glass side (rather than the window frame side and push it down/back to disengage it from the clip. Once you've done one clip it becomes really obvious and you'll have no issues with the others (hopefully).

Once the chrome trim was off, I cut the seal away from mine as lee g described - one man job and it didn't take long. My seal was original and had been re-sealed with butyl once before and it was no wonder it was leaking. I'd definitely recommend replacing the seal with a new one.