If you send a new version, I would recommend to do either of the following (from best to worst):
- Add an (autmotatically generated, i.e., reliable) list of all differences. If you use LaTeX, then
latexdiffcan be very useful for this; if you use MS Word then I assume Word has some mechanism to display differences across versions too (but I am not sure). - Send an additional "attachment" instead (giving the correct proof of Thm 2.3), and ask to ignore the proof given in the paper.
- At least, only change the (single) part that absolutely has to be changed (proof of Thm 2.3) and nothing else, do not additionally correct typos on the way or improve the presentation.
Note that 2 and 3 are more reasonable if the change is very localized. If a string of Definitions and Lemmas leading up to the proof has to be changed, got for 1.
It is not enough to just say "We completely rewrite the proof of Thm 2.3, adapt the according definitions, and fix several typos".
Reason: For a careful /detail oriented referee who already went through 20 pages and who checked for correctness, clarity, typos.., it can be frustrating to be told "Hey, look, here is another version, which may or may not be similar to what you read before, but who knows? In any case, the proof of Thm 2.3 is now correct. Have fun!"