Once you get to level X in a class you are able to edit your loadouts and trade some items off for others provided you don't exceed the number of 'slots' you have. Eg you may want to drop to a single bandage and carry an extra s-mine as a spotter/sniper or may want to carry extra bazooka ammo at the expense of some standard ammo. But only once you have worked up through the levels for that class.