Purchase Wicked Armor for 2400 carbon pickups from the 'Shop' window.
To be able to buy Wicked Armor you must first purchase Good Armor (600) and Super Armor (1200) meaning the total price is 4200 carbon pickups. One complete playthrough of the game will get you enough pickups to upgrade one weapon. If not, replay level 5 to boost your totals.
Thanks to JohnnyRock84, tastefulmrship