:saveas newname saves the buffer with the new name, makes that name the current buffer and sets an alternative buffer to the old file.
:call delete(expand('#')) then delete the file associated with the alternate buffer.
You can easily turn this into a team with something like
:command! -bang -complete=file -nargs=+ Rename saveas<bang> <args> | call delete(expand('#'))`
. , .
-bang Rename Rename! <bang> !, , . :saveas.-complete=file , , :e :saveas do.-nargs=+ , :Rename ( ), . <args> , :Rename. , :saveas, - :Rename ++enc=latin1 newfile, latin1.