Upgrading Weapons in PFS?

[Alarid]

I've been trying to find if weapon progression exists in PFS. For example, I have a +1 Steel Heavy Shield, but I want a +2 Adamant Heavy Shield of Bashing. Do I have to sell my weapon, and buy the improved version, or are there some weapon qualities I can add onto the original weapon?

[blackbloodtroll]

Relevant thread.

[Dhá Sciath]

That's exactly what I need. Thanks.