Alright, you CANT change the binding of the move/primary/interact and secondary attack (fixed as left and right mouse click). But you can define the action bar buttons as you like - also mouse wheel works.
Key Bindings Overview
See Actionbar at the bottom, the first 4 buttons refer to Action Bar Skill 1-4 and the last two are the Left and Right Mouseclick (as indicated by the symbol)
You have to enable Elective Mode to be able to place skills wherever you want to, else they are restricted to categories (good for newbies so they always have a somewhat decent skill set active)