If you are asking about claiming premiere tickets, there is an online auction for them, but the prices often go up to ridiculously high levels, so unless you're a multi-millionare, I doubt you'll even want to try. If you are wanting to claim tickets for opening night or other at your local theatre, however, just call them or go there and ask for showings, dates and times, and reserve however many tickets you need. There may or may not be a holding fee. You can also get tickets online through Fandango and other such sights.
Get tickets for HP7 online
Search "wizarding world of harry potter" click on the first link and you can buy the tickets on that website easily!
.. At a movie theatre.
Yes you do.
yes
Most likely.
Go to fandago.com or ticketfinder.com
one of your local (opptional) movie theaters
about 1,000
Harry Potter defeated Lord Voldemort on multiple occasions and won the second wizarding war.
fandango.com/harrypotter
luck