I'm trying to find a story I read a while ago. As far as I can remember, it was a LitRPG ebook based in a world where increasing levels actually took you to a new section of the world.
The main character had reached level 100 (I believe) and found a ring that began removing his levels, slowly sending him back down the regions of his world.
This might be Negative Man by Outspan Foster
Davin Pentcross has achieved his lifelong dream of being a level one hundred adventurer on his homeworld Eternity Ring, a massive ringworld in which strength and a person's level dictate how society functions. But Davin is old. When he loses everything he holds dear, Davin discovers an odd ring in an ancient dungeon. The moment he puts it on, he loses a level. In exchange for returned youth, the ring saps his powers and makes him lose a level everyday until he is killed or becomes a level one again. In a world where a person's level means everything, Davin is doomed to become weaker and must use his experience to survive the harsh world of the Eternity Ring.
I found this by searching for litrpg ring "level 100"
