Change floor level with mouse

I remember having been able to change what floor is displayed with my mouse, possibly combined with some hotkey like alt or shift. Coming back to the game after a long time, I now seem unable to remember how, and changing floor seems stuck to page up/page down. Unfortunately I don't have page up/down on this keyboard, which makes changing floor level quite annoying.

Anyone know how (or even if) its possible to use mouse buttons for this?