You may not see the 'imagesupload/cms_files/' folder on your local machine (unless you have downloaded it from your remote server) - it will have been created on your remote server as part of the set-up process. If you look at the directories and files on your remote server you should be able to find it.
You could try puting the absolute server path between the '' at about line 50 of the config.php file
$Config['UserFilesAbsolutePath'] = '' ;
To find the precise absolute server path to your folder, create an empty php page and paste in as the first three (and only) lines:
Save the file as ab_path.php and upload it to the inside your imagesupload/cms_files/ directory. Once you have done that,use your browser to navigate to that file on your remote server, and make a note of the absolute path that should be written to the page. It should begin with a forward slash.
So your line in the config.php would be a string something like:
$Config['UserFilesAbsolutePath'] = '/home/users/uks48634/html/somesite.com/cms/files/cms_files' ;
That may or may not work, but worth a try . . .