ok, experimentation. It is not necessary to delete all time
When I make a change in the XDK project, even if it is just adding a line in the script (.htm or .js) and when START BUILDS, always, always have to delete upload project files from source build server?
Or is it not necessary?
You do not need to delete the files on the server. That feature is there in case you prefer to not leave them on the server, but they are associated only with your account and will automatically be deleted after ~30 days (I don't recall the precise time).