Open the reservation via the 'Reservations' module, or search via the general search bar in the top right of your screen.

Click on the pencil icon next to 'Stay', in the 'Reservation' block. Here you can adjust the departure date.
You then have to make a number of choices for updating the reservation.

Update the rent

Choose one of the options below.

Add only the rent for extra nights

You charge the current nightly rate for the extra nights, and add that to the original rental price. This current nightly rate may differ from the nightly rate for the stay as it was originally booked.

Recalculate the rent for the entire stay

The cost of the entire stay is recalculated based on the adjusted dates. The current prices are applied. This option is often used for significant changes in the length of stay.

Do not update

You do not charge for the extra or fewer nights. The rental price remains the same as before the change.

Update the cost items

Choose one of the options below.

Update only the quantity for per-night cost items

The prices of the cost items on the current order remain unchanged. The cost items that are charged per night are adjusted based on the new length of stay.

Update cost items for the entire stay

All cost items are recalculated based on current prices and the new length of stay.

Update the security deposits

Here, you have a similar choice between recalculating and reapplying the current security deposit policy, or not updating the security deposit and thus leaving the current application of the security deposit unchanged.