Using any Armor Piece (Back, Arm, or Sub) go to the Item Lab in the shopping plaza.
The armor pieces are the purple pick ups (they have purple backgrounds on their image)
You'll need a handful of Meseta and Grinder.
Select your armor piece you want to upgrade and keep enhancing it until you eventually fail.
I spent around 12,000 meseta and 5 grinders. I failed pretty quickly.