There must be some mistake. If your project page shows the cover in the sidebar, it means you don't have screenshots uploaded. You should upload screenshots. Also, is the new game cover visible on your profile, and in game listings / searches?
https://k-storm-studio.itch.io/ghost-warrior
this one. That was just a old covert art and there is no way to replace. Basically at the moment there is not cover art set but it's still exists in the official page.