Titan Quest

I’m writing a hint because I noticed that some people don’t understand what needs to be done to achieve the achievement.
To complete this trophy, you need to take extra. quest "Legendary Mastery" from Dvalin and Dulin in the halls of the Dvargrs. Follow their instructions and at the end you can upgrade a legendary (purple) or epic (blue) item. I upgraded the epic item as normal, since there were no legendary ones yet. They gave me the achievement.