Hi Lustfull6549, if you're playing on Android and using the on-screen D-pad, you should be able to hold between for instance the Left and Up button to get a diagonal input. That being said, it's still a little tricky to get the right spot.
Just tapping the up/down button while moving is going to be nearly impossible though, because you need to be holding the up/down button when you exit the area before the staircase. So if you can't get the diagonal spot working, you might be able to use 2 fingers to hold both directions while you approach the staircase.
Hope this helps get you unstuck for now, and I'll see what I can do to make it easier for next release!