I have found similar topics, but none of the answers helped me.
I have installed Elementary, but the amount of bugs on it was atrocious, so I wanted to move back to just regular Ubuntu (Yeah, I know they have the same kernel and what not- but on Elementary things like the clock, wifi aren't working and they were working perfectly before). I managed to get my log on screen back to Ubuntu and delete all the apps, but I still have the KUBUNTU screen when turning on the laptop and have the Elementary in the settings as my system.
You need to remove Elementary from Sessions to prevent it to list while turning on your system.