Is it possible to upgrade armor in Witcher 3? I have tehsan mutna armor, and I am playing new game+. I have the armor from previously imported game. However, the armor needs to be scaled up and is useless as is. Is there any way I could re-use this armor or just find a better armor instead? I have the set and I wanted to keep it. Sucks!
Yes, it's possible to upgrade armor.
First, you'll need to find a Diagram. I'll link you to a wiki with all of the Diagrams for armor: https://thewitcher3.wiki.fextralife.com/Diagrams
Next, find an Armorer and select the armor that you want to upgrade. It will require specific materials, but when you upgrade it, the armor will progress to another tier. Upgrading armor is beneficial to its stats.
The only items you can upgrade level-wise are the various witcher sets, up to level 55 since you have the Blood & Wine DLC.
Unique sets like the one you mention get around the level you have when you find them. You can't upgrade them, so they will not scale well when you level up. You can of course use runes etc but that only does so much.