Upgrade, as in infusion? If so, take a closer look at the season symbol in the corner. If it's a white symbol on dark background, it can be infused. If the symbol is dark on a white background, the piece has a Light level capped, and it goes as sunset. You can't raise its LL past its cap value.

It cant be fixed without more info. Is it power capped armor? is the slot missing? is it legendary/exotic? which pieces is it?