Hilton HHonors - Can you change your award level in middle of your stay?

If I book an AXON and decide on day two I want to stay 6 nights instead of 4 can I change it to the 175,000 mile award?
Thanks.
D.

First question would be to find out if they have award rooms available for the extra days. If they do, I would talk to the hotel manager and call HHonors.