There are several options for getting up the tower, including making a restaurant reservation (which gives dedicated elevator access), taking the elevator and taking the stairs. We found the line for the stairs much shorter than the line for the elevator, so that's the option we took. It's a less strenuous journey than you might think, and we were up on the first level in 10 minutes, and then walked from the first to the second level in another 15 minutes.
There's a place to buy drinks and snacks on both levels.
Once you're on the second level, it's possible to buy a supplementary ticket to go to the very top. Note that if you do this you appear to have access to a separate (and much shorter) line than for those who bought their to-the-top ticket at the same time as they bought their other tickets.