To unlink a subaward from its prime proposal, open the prime and go to the Subaward Budget Attachment form. To the right of each subaward in the list you will see the 
Icon . Click that to be taken to the following screen:
Here you can choose to simply unlink the subaward, returning it to the Proposals List for later use, or to instead Unlink and Delete it all at once. If you delete the Subaward, no other user will be able to see or use it.
After unlinking, all Budget Data, Key Persons, and Performance Sites from the subaward will be removed from the Prime proposal.