How do i level up a weapons level?

[EASY PETE]

[Justinyl]

level yourself up

[Mayo]

You can't. As your player rank goes up, gear ranks for items in the world will scale to match until rank 6. For ranks 7 - 9, you will have to fight special infected, or just go loot sunken airdrops.

[Leaves]

If you advance and level up your Parkour and Combatskills you increase overall rank, (you can see that on inventory screen top right corner)
If you advance, Itemlevels are also advanced. You'll find higher Lvl Equipment and can buy higher Lvl Equipment from Vendors.

[PlevisVesel]

You don't.
What's worse, dropped loot doesn't go above LVL6 even if you are above LVL6.
And the quest loot is at fixed level. Meaning you can complete a quest being LVL7 and get an artifact weapon that's LVL3 and thus completely ♥♥♥♥♥♥♥ useless.