Achilles: Legends Untold

You can upgrade a weapon to Level 15 by the end of the game, but you will need to wait a while to do so. The initial blacksmith locations only go to Level 9 and then you'll need to wait until you reach the Greece Coastline and he'll move there and be able to upgrade your gear the rest of the way. You won't be able to find the final bronze upgrade items until you reach this location either.

You will need bronze items and money to level up your gear. You'll find the basic type in the earlier locations, the next type mid-game, and the final type toward the end (naturally). You'll also need crystals to upgrade certain types of gear, such as specific crystals for a specific attribute attached to it (i.e. Poison Crystal for a weapon that can poison enemies). Upgrade any weapon or armor to max to unlock this achievement - I would highly suggest going for the weapon as damage is much more helpful than the minor resistances and damage mitigation that armor provides.