First of all you'll need to download the game in .ISO format from a trusted source, obviously. Then you'll need to extract the files and folder from that .ISO using ISO Extracting Tools or Programs. Then when that's done, you'll need to transfer that folder to your RGH inside XexMenu, Games Folder.
1) Download game from [ Register or Signin to view external links. ]
2) Download Jdownloader 2 from [ Register or Signin to view external links. ]
3) Download Xbox Image Backup from (Google)
Jdownloader is a download utility tool that helps you download files from downloadgamexbox.com and extract them files into a .ISO file, then you can use Xbox Image Backup to extract the files and folder from the .ISO file and when that's done you just put the folder on a USB and transfer it to the console.