[Jstylezzz]

What do you mean by 'saving' files 'in Bitvise'? As Marcel said, it has a client built in that uses sftp which allows you to upload files to the server you're connected with (as long as the server you're connected with supports sftp / has sftp enabled).
If you upload your .amx to the SA-MP server's gamemodes folder, you can simply restart the server through command line and it'll be updated.