Originally Posted by BaBaBoOeY
Trials does not use a save file stored on the xbox as all your progress data is stored on the Redlynx servers.
So you should be able to just delete the entire directory from your HDD then re-download Trials and any DLC you may have purchased for it and then carry on from where you left off.
NOTE:
If you have created any levels or have saved any favourites in the editor which are located in that directory then i would suggest moving those files to a xbox formatted USB stick before deleting the entire directory or you will lose them forever.