If you're trying to set the 1-10 keys down below, go into the menu where you change your main 3 buttons and the secondary pallet (can't remember the option's name) and select one of your attacks AS IF THOUGH you want to change. When you scroll over the attack (or item) that you want to assign to a number key, instead of pressing "Enter" just press the number. It should appear next to the icon and be assigned.
I have never found a good way to explain this, so I hope it helps.
Edit: I totally misunderstood what you were asking. Oh well, I'll leave the above post as-is. Hopefully it helps someone :3