What increase next levels trap?
For anyone who didn't notice...
On every object that can be leveled-up, you can tap the object and tap the Info button and the two strengths an object can have
Heart = ability to withstand attack
Sword = ability to attack
are shown with a bright and a dim progress bar. The dim portion shows how much more ability the upgrade will give, and that's also shown as the +number on the right.
Unfortunately, most rooms have a large bouncing shortcut button that will take you directly to the Upgrade feature, so be careful not to tap that. Just tap the room to see the panel with the Upgrade and Info buttons. Luckily, the traps have no shortcut button. I have no idea why anyone thought to hide the dungeon under all these stupid bouncing shortcuts that only confuse the interface.