You can change the number of guests for a specific reservation through the Reservation page. Follow the instructions below.
For Vrbo reservations, the number of children cannot be edited.
Step by step:
Sign in to your Guesty account.
From the top menu, click Reservations.
Click the relevant reservation.
To the right of "Summary", click the pencil icon.
Under "Guests", use the arrows or click the current number of guests to enter a new one.
Once completed, a recalculation of the reservation's price is triggered. If calendar prices have changed for the dates in question since the reservation was created, that will be reflected in the new accommodation fare.