By default, this is not possible, as you can't change the Event on the Attendee profile.

The best solution is to cancel the registration, refund the ticket, and ask for another registration for the second event. 
This way you keep your accounting clean.

Alternatively, you can manually register the attendee information on the second event, Ticket Sales will mark this as a "FREE" ticket. 
Send the ticket information back by email / SMS.