How to upgrade weapons? (Sword Art Online: Fatal Bullet)

the killer of the Anglo-Saxons
Not sure that will help answer this, but better weapons is happening in the room from Kirito Lisbeth. The number of unlocks for each weapon is limited and depends on the initial level of weapons - so if it is the first level, the only improvements you can make 5 (with all updates until like 8 rose, but not sure); and for weapons 3 levels, respectively, only 2 (or 5 with upgrades). Therefore, if the right weapons are not visible in the selection menu to improve, it means that the limit of improvement has been exhausted.