Hi,
You can’t, there’s not such option. You can create a manual reservation or the guest can cancel his reservation and create a new one.
However, this is a great idea and I will try to add this feature in the next updates. Unfortunately I’m really busy right now so it will require at least a couple of months.
Anyway, can you explain better your situation? Does the room require a deposit? Does it contain a non refundable room?
A solution can be:
– Only for pending reservations (so no reservations with deposits) the ability to modify the dates (if they are available of course). Both for the admin and the guest. The guest may be able to modify a reservation only if enabled in the Hotelier settings.