This is not currently a feature in Sphere.  In order to move Sponsorships from one event to another you must remove the Sponsorship from your event and recreate it in the new event.

If you are creating the sponsorship:

1. Go to Communities > Special Events > Friends Asking Friends > Kintera Thon
2. Select your event
3. Click 'Utilize Bookkeeping Tools'
4. Click 'Single Sponsorship Entry'
5. Use the search bars to locate the sponsor whose sponsorship you are moving
6. Fill out their sponsorship amount, level, and other details
7. Click 'Save'