Rename
From Scriptwiki
Renames the specified file or directory.
/rename <filename> <newfilename> /rename <directoryname> <newdirectoryname>
Can also be used to move a file from one to another directory. If the filename contains spaces, you need to use double quotes. If no special path is given mIRC assumes to find the file using the mIRC directory as basedir.
Example
Renames "foo.txt" to "bar.doc" in the mIRC directory.
/rename foo.txt bar.doc
Renames and moves "C:\My Directory\foo.txt" to "D:\bar.txt"
/rename "C:\My Directory\foo.txt" "D:\bar.txt"