You can use 1 Minor Action to change the armor’s type (i.e. Chainmail, Full Plate, Breastplate, etc.) to another type. This also changes the armor’s appearance to match its new armor type. This is a transmutation effect on the armor, not an Illusion effect, and the armor grants all of the effects (both positive and negative) of its new type. The armor reverts to its original type and appearance when you take it off.
You can spend 1 minute of concentration to shrink the armor down to a necklace or bracelet. While in this state, it offers no benefits as armor, but you can use a Free Action on your turn to return it to its original type of armor.