1. Download the file and extract it using whatever you use
2. Open the folder where you keep Sonic Worlds
3. Go to mods
4. Go to MenuThemes
5. Take the contents in the file you extracted (Background, buttons, etc) and copy and paste them into either CustomTheme1 or 2-8
WARNING: IF YOU HAVE A THEME INSTALLED IN ONE OF THOSE FOLDERS, IT WILL REPLACE IT. BACK UP THE EXISTING THEME MOD YOU HAVE BEFORE REPLACING!
6. Open Sonic World and go to settings (Make sure you have mods and debug mode activated)
7. Go to Menu Theme and go down to Custom Theme what ever number you chose.