Engine, pilot protection, and wing changes to the Wildcat

What modifications did the British make to the Wildcat?

They increased engine performance, changed the pilot's protective backplate, and altered the wings.

The changes covered engine performance, the plate behind the pilot, and aspects of the wing design. The resulting Wildcat is judged substantially better than the Buffalo, whereas the earlier aircraft had been narrowly beaten by it. Its ability to accept changes explains that improvement.