Note: make sure you are logged in and in the correct event.
This article explains how you can add a participant currently on the waiting list to registered and let him participate in a full event.
Go to the participants with status "Waiting" and find the participant you wish to add.
Under Actions, "Change Status" of participant to registered
Manually change the participant status into registered.
Find the participant using quick search or advanced search or look for him/her in the 'registered' tab. Click on actions, and email.
Send the participant manually (usually this will happen automatically) an email with the request to finalize their registration.
Participant finalizes registration and pays the products and activities required/chosen.