I have a legendary weapon that I have been using for a while and it has some really good perks that work well for me. The problem I have is that the gun is now 15 levels lower than my current level and the base weapon that is not legendary has better damage now compared to the legendary one. Is there a way to increase the level of a weapon to improve the damage?
Unfortunately not, the weapon levels are fixed. It is a problem you are going to come across many times in the future. You will get a great weapon but the level is not for you. You have two options. Sell the weapon to a player that is the right level for it or just get rid of it at a vending machine for some scrip.