@Charles79, if it is an entire account you are taking down, from your laptop/desktop go to Account Settings (under your name at the top right), click Settings then click Cancel My Account. That is explained in Help, so you can check there, too, to get more information. But that's your step-by-step.
@Charles79 You have been given good help from @Lawrene0 however, I would urge you to make use of the Air BNB Help Center as well for such basic questions. I have seen hosts provide incorrect information (we all make mistakes and are learning as well) so the information about how this platform works really comes from Air BNB. Please take time to become comfortable with seeking information from the Air BNB Help Center. Good luck!