1st, what are the details of the flight you want to UG. City pair - fare class of the ticket you are holding.

2nd, what do you mean by credits? A Delta $$$ ECV? SkyMiles? Other?

Any additional details would be helpful, but you didn't supply ANY!

So, to answer your current question: Maybe. (same as above)

edited to add:

It sounds like you may be referring to an UG offer from within your existing reservation, as your lingo above sounds like something from DL.com?!?