Your gear levels increase by opening silver treasure chests. So you'd need to seek out the silver chests on each floor.

As for being stuck, if you talk to the Wood Wailer outside, you can select "Reset Progress" and it will return you to floor one, and reset your character level to 1, but your ARMOR/WEAPON LEVEL WILL REMAIN.

So if you're stuck, starting over will help. You'll have to get your character level up again, but your equipment will keep their current boosts and you can just keep increasing them. So by the time you get back to where you are now, you will be much more powerful.