Rare 

go into faction guardians, select on the slot the champions you want to remove are in, click on them so that they are no longer highlighted green, and hit confirm

Carpe has it! Let us know if you have any more trouble.

Thankyou thats sorted it.

Help, I have the same problem, I am quite new and have a hero in the Guardian Ring but can't see how to get him/her out !!! I've clicked on the Faction Guardians tab but there's nothing in any of the options !!

i

click on him so it brings up a list of champs you could place there. just unselect him, and hit confirm

Alternatively, if you try to select him for any campaign or dungeon content, it will ask you if you want to remove him from the sparring pit.

Necro post is very necro today.