How is this possible? I have someone under the name of register and I cannot remove them.
Sorry about the late reply, but I stumbled on this thread while looking for answers and wanted to share my findings. I hope you have a "better late than never" attitude, because I found out how to remove friends. According to this thread ...:
... blocking another user will prevent them from following you. To block someone, go to their profile and hover over the little nearly invisible gear next to the "Languages" box. This gives you the option to "Block [username]". After fiddling around with the "Following/Followers" box on my profile page, I found that blocking someone will remove them from your Followers if they are already on the list.
I hope this helps. And if it doesn't I hope you don't have to wait another seven years for the answer.
That depends on whether you want to unfollow them, or them to unfollow you. Duolingo makes a distinction between people you follow ("Following" in the box on your profile page) and people who follow you ("Followers").
If you want them to unfollow you, blocking is the only way to do that as far as I can tell.
If you want to unfollow them, go to their profile. You will see a green box containing a tick mark and the word "following". Click that to unfollow them.