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 there are some screws on the frames, you can use the tiny screwdriver to unscrew them, then you can pop out the lenses easily. If your glasses frame is plastic, then you should directly press the round part of the lenses by force, and then the the lenses can be popped out.