Upgrades work differently than you might expect - they're all available right from the start with no mission requirements. Check the service shop regularly, where upgrades appear randomly based on luck. Core improvements like stamina, health, sprint speed, and strength can be purchased whenever they show up, as long as you've got enough cash on hand.

The prices scale up when buying multiple of the same type, so plan your purchases carefully. Just remember that everything's driven by shop rng and your wallet, not story progress or achievement hunting. Pretty interesting actually, since this setup lets you focus on whatever stats match your playstyle right from the beginning.