In order to properly uninstall the demo of Drive Genius 3, you will need to manually uninstall it.
To manually uninstall Drive Genius 3 delete the following files and folders at the end of the paths listed below. Double click on your "Mac HD" drive to start the path.
/Library/Application Support/DriveGenius (folder)
/Applications/Drive Genius 3.app (icon)
If you are running OS X Lion, Mountain Lion, or Mavericks the last three files/folders are located in the Users Library Folder which is hidden in the operating system, You can temporarily access this folder by opening a Finder Window and pressing Command+Shift+G. This will bring up "Go to the folder", enter in "~/Library" and click go.
/Users/Library/Application Support/DriveGenius (folder) /Users/Library/Preferences/com.prosofteng.DriveGenius2.plist (file)
Now you will need to restart your computer.
You can contact Drive Genius support at (877)477-6763 [press 2 for support].