arrows. left (mouse) click and hold , dragging them over a clear area of the screen. click the 'control' key. let go left mouse and designate number wished to drop.
this also works with potions, gold, etc. and is a good way to sell some of something to the BF merchants.
there is no way to remove chams once they're inserted.
in-game, the highest number of slots on any equipment/weapon you'll find is 4.
don't be blinded by slots though. many of the best items have only 1 slot or even no slots at all.
there are a couple threads regarding charms and their values. if you don't know this stuff yet, let us know or use the 'search' function.