Removing the lenses from a pair of glasses can be accomplished without breaking the lenses or the frames if you are gentle and careful.
Determine what type of glasses you have. Do your glasses have a screw that will open the frame and allow the lens to fall out? Are your lenses solid and have no obvious way to remove the lens without force? Are you sure the lenses you are removing will fit into another pair of frames?
For a plastic lens, attempt to wiggle the lens to see how snug the fit is. Older glasses may have become loose with wear and the lens may slide out with minimal pressure. DO NOT FORCE THE LENS OUT.
For a frame with a screw, use the tiny screwdriver that comes with a glasses repair kit to open the frame. Be careful not to strip the screw when you remove it. The lens should fall out as the screw is loosened. Be sure to do this over a soft surface so the lens does not crack.
If the lens is held in the plastic frame tightly, you will need to gently warm the frame in order to get the lens out. You can do this with a blowdrier or a bowl of hot water. Do NOT use boiling water!
After heating the frame for one minute, attempt to use remove the lens gently. Do not force it out, you may break the frame.
If you are still unable to remove the lens, return the lens to heat for an additional minute. You can also use hotter water as long as it is not boiling, as you can melt the frame.
If you are still unable to remove the frame without using force, you can visit the optical shop where you purchased the glasses and request their assistance.
Work over a soft surface so the lens does not crack when it comes out of the lens.
Use a cloth to handle the frame when it is hot.