You may carry only one Big item. (Any item not marked Big is considered Small.)
You may not discard one Big item to play another; you must sell the first Item, trade it, lose it to a Curse or Bad Stuff, or discard it to power a Class or Race ability.
If something lets you have more than one Big item (for instance, the Dwarf race) and you lose that ability, you must either correct the problem immediately or get rid of all but one Big item.
If it’s your turn and you’re not in combat, you can sell the excess Big items (as long as you have at least 1,000 Gold Pieces of Items to sell). Otherwise, you must give them to the lowest-Level player(s) who can carry them! If any Big items are still left over, discard them.