If you are considering selling your boat, you should pay close attention to the requests you receive from that point on.
This is because from the moment you accept a rental request, you are committed to fulfilling it and making your boat available to the renter, who in turn is reliant on you.
Once the reservation request has been accepted by the owner, the owner is obliged to respect the commitment made at the time of acceptance of the reservation request, except in case of unforeseen circumstances (force majeure).
Simply deciding to sell is not considered as unforeseen circumstances (force majeure).
If you want to know more about cancellations : Can I cancel my reservation? and Can the renter cancel their reservation?
If you wish to delete your ad, you can do so by following the instructions in this link.
Finally, to place a new ad following the purchase of a new boat, simply create a new ad via your account, in the "My boats" tab.