The route is very obvious: You walk up where it appears flat and easiest. There is no fix route and there will never be a track, especially in the upper parts: There you have to find out yourself, how to circumvent the crevasses. Once you reach the crater rim, a short passage to the left will carry you to Haakon VII toppen, the highest spot.
This only applies in excellent weather. The slightest question mark in that respect means you have to postpone any activity. Until your time on the island runs out ...
"So I was sitting in my cubicle today, and I realized, ever since I started working, every single day of my life has been worse than the day before it. So that means that every single day that you see me, that's on the worst day of my life."
--Peter Gibbons (Office Space)