Welcome to Flyertalk.

You can give them a call and ask what they can do for you. If there's a non stop available they may put you on it, or they may offer you a full refund.

Not sure there would be any difference in fare to recoup.

It's going to depend on how much different the new flights are, if they leave and arrive within a few hours of what you had scheduled they may do less than if it's a significant change.

Or as they say

CONDITIONS APPLY

If a Delta schedule or routing change has delayed your departure or arrival by more than one hour, you may be eligible to select an alternate flight at no additional charge. Note that the below conditions may apply:

Your origin, destination and travel date must remain the same
Alternate flights must be available, and you can only modify once as subsequent changes may result in additional fees
Voluntary changes to other flights not impacted by a Delta schedule change may result in additional fees