Arthur, if the beads are on the inside then you need to remove the bead by putting a thin pallete knife in the centre of the bead opening the gap where the bead joins the frame (not near the glass). once it lifts slightly then its easy to work it out.
If the beads are on the outside then the rubber gasket is just a wedge and can be lifted by putting a pallette knife between it and the frame and lifting slowly. once a small portion is up it will come out easily. Have someone on the outside ready to remove the beads as per previous description and then take out glass. Have one hand on the outside on the glass at all times to prevent the glass moving the beads out suddenly. you will have to measure it then put back to order the glass thickness also.
Russ
May 2008