To upgrade your weapons in Prince of Persia: The Lost Crown, you need to find a special NPC and get a rare currency.
Prince of Persia: The Lost Crown isn’t the most difficult game in the world, but it does offer its fair share of tough fights. Especially the boss fights. To make things easier, you can upgrade your weapons a few hours into the game by finding the NPC Kaheva.
Prince of Persia The Lost Crown: How To Upgrade Your Weapons & Amulets
To upgrade your weapons, you need to unlock the NPC Kahvea in The Haven. Her forge becomes available after progressing the main story in The Lost Crown far enough. This should take you only a few hours.
From then on, Kaheva will upgrade your weapons and amulets in exchange for Time Crystals. Weapons also need Azure Damascus Ingot, which is pretty rare and mostly found in or around the main path of the game. Amulets eventually need Xerxes for further upgrades, another rare resource in the game. Check out this guide to read everything you need to know about Xerxes: