For NPCs: Gather the required materials, get enough money for the upgrade, then enter a town area. Upon exiting, they will likely have upgraded their equipment and/or cloned accessories if BR is high enough. A much slower way is just gathering enough money to purchase the necessary materials, including drops. The materials available for the other units is bound by story progress. For Rush: Really straightforward. Gather the materials, have enough money, have the right customization rank.