I found another proof of my theorem. Can I present two different proofs in the paper? My area is mathematics. I have just found another proof of the main theorem in my paper. It is slightly more elegant than the previous proof that I wrote, but the idea is very different. When submitting this paper, can I include two proof in the paper, or must I select only one? Personally, I don’t want to delete either of them, but I don’t know how the editor will deal with this situation.
If the two proofs are sufficiently different, then it's entirely reasonable to include both of them in your paper.  You might, however, want to think first about whether the proofs might actually lead (easily) to different generalizations of your theorem.  If they do, then you get two benefits: It's then clear that the two proofs are genuinely different. And you have some more general results.