So, on with it! Open the folder you extracted XoopsInfo into and find the /phpsysinfo folder. You will also see /class, /kernel, /language and /modules. /class, /kernel, and /language make changes to some of the core XOOPS files, so I recommend leaving those alone and not adding them to your site just yet. Copy the /phpsysinfo and /modules folders to your root. You will get a warning about the /modules folder already existing, but you can safely copy this folder over your existing /modules folder. It will only add the /xoopsinfo folder inside the /modules folder, adding it as a module, just like you did with XOOPS DB backup and restore.