$url = \'http://site.com/images/name.jpg\';
Its a full path for the file, which is already exists on ftp.
How can I change file\'s name
As others already point out, the PHP function you're looking for is rename, but you can't rename a file through a http:// URL (At least not in PHP - As @Artefacto says, WebDAV can do this.).
http://
You will need to specify a proper filesystem path.