As I've been asked this several times, I thought it about time to save my breath and write down some guidance. This is in addition to the official Lewmar guidance note which can be downloaded by clicking below.
Now, having done a few recently...
The pins are stainless, the frame is alloy. Lewmar do apply a black coating to pins to reduce corrosion but as earlier examples can date from 1992, this may have passed its prime.
In theory, you remove the small plastic plug inboard of the hinge, insert a suitable tool (eg flat head screwdriver) and lever the inboard end of the pin outward for approximately 15mm. Then using some small mole grips you grasp and twist the now exposed outboard end and remove, being careful not to lose the plastic washers on either side of the lid hinge part. Simples...
In practice, your pins are probably corroded in position, so the first task is to help ease and lubricate. Before starting, look at the pins to see which is less embedded in the frame (see next step) and concentrate on this. Take a heat gun and heat either side of the lid hinge part. Then apply some fluid. Releasing fluid is great, but white spirit will do. Hopefully these will ease the bond between pin and frame.
While hot, your first challenge will be to get the tool around the end of the pin as invariably the pins are pushed in too far (take note not to repeat this mistake when reassembling). Try a very small tool.
Assuming you can get some movement, try to lever the pin out. Once part way across the hole cavity you may find using an 'L' shaped tool (eg end of an allen key) to lever more of the pin out an easier option. You really need to push the pin head fully across the cavity so you will have enough exposed pin to grip next.
Now apply the mole grips and remove the pin.
At this point repeat for the next, but if not going well, switch to Plan B.
Plan B: The channel for the pins runs across the whole frame, so you can insert a suitable drift in the side you've removed to push the other pin out. You will need a 5/6mm steel rod of ~45cm length. So equipped, you can apply more pressure using suitable hammer. Remember to protect the frame from the hammer.
Of the ten hinges I addressed last week, only one hinge refused to budge and because we didn't want to risk breaking the weld we gave up and refurbished with the base attached. Not ideal, but better than a broken weld.
Best of luck!
Remember not to push the pins all the way in when replacing!