Thank you! I'll try to do the background brighter.
You should brighten up everything. The background is not important. Being able to see the ground and walls clearly is important. If you only lighten the background then the contrast with the ground will be even lower.
If you want it to "feel" darker after you lighten it up, you could try adding more shadows to the artwork. You could also darken a bunch of the cosmetic stuff a lot, like the skulls. 1) This will make it much easier to see the important things (like spikes), and 2) It's more accurate - white skulls will not appear bright white in a dark dungeon.
A little mockup (left) compared to your original (right):
[Edit] I just found that at least some of these are
prefab assets. But it seems like you changed their brightness a lot yourself? Either that or maybe the contrast on your gifs is really messed up somehow?