At any point in the game, press
to go into your menu. Under the suit tab, you have 5 categories that each hold 4 upgrade perks for frag grenades, ice grenades, etc. Using the praetor tokens found throughout the game, you must unlock each upgrade perk for just ONE of the 5 categories. For example, under frag grenade, you'd upgrade the following:
Faster frag cooldown
Combustion concussion
Scatter bombs
Frag stock up