There are two options to get there. The easiest, but far less beautiful option is to take a taxi. For a few dollars, a taxi will drive you to the top and wait for you while you take photos.

The best option is to walk. The walk takes about 20 minutes and, I warn you, it is all stairs. But it is worth it. The views are amazing and the walk isn't all that difficult. There are plenty of places to stop along the way and countless photo stops. Bring a lot of film! It's also a great place to be alone, as not so many people are willing to make the climb. I often bring a sandwich and a book and have lunch perched on one of the walls overlooking the city. The church is only open for weddings, so you might walk all the way up and not be able to go inside. The remains of the Castello are almost always locked. But frankly, it's still worth the walk. Once you get to the top, you'll find a small restaurant. The food is good and it makes a nice rest break from your climbs.