We are trying to install the rear quarter glass in a 1967 Chevy Convertible but are having a hard time getting the old one out. Do you have any suggestions on how to remove the old glass? The instruction manual doesn't say how to do this.

do you have a Fisher body Service manual for 1967?
The info would be in there.

Camaro's, Nova's, and other models with a single track regulator it's easiest to remove the regulator, track, and glass all in one peice. Full size cars and A bodies are possibly different.
Exactly what are you working on?

Whatever chevy it is, if the body style didn't change much 67 to 68, I have a 1968 book I could check for you.