Remove trim, bumpers etc. as required. It can make the job easier in some cases if the bulk of the old panel is cut off first with a sharp chisel, leaving the welded areas much more accessible. Make a quick note of where and how it's welded, so that the new panel can be welded in the same places. (Note: some wings may be welded on to raised mounts, making weld position important!) Now each spot weld needs to be located and cleanly removed. Purpose-made spotweld drills are available for this, which work on the basic principle of a hole saw, cutting around the weld button to separate the two panels. Where access is limited, a sharp chisel can be used to carefully cut the outer panel only, leaving the bulk of the spotweld still attached to the underlying panel. It is much safer to leave excess metal on the supporting panels, as this can be cleaned away later- much better than not leaving any metal to weld too!
Whichever method you choose, the most important part is not to cut away the supporting panel or flanges that you will need to weld the new wing to. With the bulk of the old panel removed, any remaining bits of panel or spot weld studs can be easily ground away with an angle grinder to leave a smooth, clean surface. With all mounting edges clean, check for damaged\twisted areas caused during the removal operation. Once you are satisfied with the results, try the new panel in place for fit. Genuine manufacturers' panels and most reputable aftermarket panels should be fairly easy to align, but there are still poorly fitting panels available, so it's buyer beware. Ensure the panel is capable of fitting properly before removing it again for the next stage
