in your site, create a subdirectory:
and upload the power CMS files to the PowerCMS Subdirectory
I could never get this method to work. If you move everything to another directory "PowerCMS" every time you "Add content to CMS" PowerCMS tries to rebuild the structure of the file system to the root folder again.
The code PowerCMS adds to the page does not refer to the new PowerCMS directory but to the root.