Navigate to the Event that the User is currently registered to (see view an individual Event if you're unsure how to do this).
Click on the Users tab.
Tick the box next to the User(s).
Choose Change Event from the Actions dropdown menu.
Choose the Event you would like to move the User(s) to from the popup window by selecting the radio button next to it.
Click on OK within the popup window.
The delegate will be moved and they will receive an email notification informing them that there has been a change to their booking.
They will also show as being Cancelled on the current Event: