You are kind of confusing me heh. The xml files on that page don't get uploaded. They get installed through the ACP from your local machine.
You said you have the forum installed on the root but you also have a forums directory? Do you mean the CMS is in the root and your forums are in /forums/?
If it's all installed in the root then you shouldn't have a forums folder.
Here is an example.
You have
www.mysite.com which is where both the cms and forums are. So you would have
www.mysite.com/admincp,
www.mysite.com/includes, etc. So just dump all the files into
www.mysite.com and don't worry about changing the garage_directory.php file.
If you have your CMS at
www.mysite.com and your forums at
www.mysite.com/forums then you'll have
www.mysite.com/forums/admincp, ww.mysit.com/forums/includes, etc. Upload the files like in the instructions, with the folders in the first image going into the
www.mysite.com/forums directory and the rest in
www.mysite.com. The garage_directory.php file would need to be changed to the root of your forums directory, something like /user/myaccount/public_html/forums/
If you're not sure the correct path, look in the ACP
ACP->Maintenance->View PHP Info
scroll down to DOCUMENT_ROOT
Hope this helps.