Removal of Rocker Arm

I have a 1980 450SL. It has valve train noise and one cyclinder is fouling. I want to replace the valve seals and check the rocker arms, and ball studs. However, I have never done this before and want to tread lightly so that I don't do any damage.
Would someone please give me detailed instructions on how to remove the rocker arm? I compress the spring 1/4 to 1/2" with the cam lobe up, and the rocker arm doesn't easliy come free.
Approximately how far do you have to compress the spring. Exactly how does the rocker arm come out? Thank for the help.
Lon