Click on Delegates in Extras section in the left hand menu.
Click on View delegates
To delete a registration, tick the checkbox next to the delegate and then click the Delete Selected Registrations green button at the top of the table.
Other options are available if you click on the registration you want to edit.
Click anywhere in the row of the chosen delegate to access the read only version of the registration.
Click on Edit Registration at the top of the page of the registration.
You can then edit the registration, changing any of the fields required, including conference event tickets or, if you scroll down to the bottom of the screen, select the status that you want to allocate to this registration.