Sometimes you might need to remove a character from the scene. To do this:
1. Hold Alt and double-click the Animation Track that contains the character
(if the character occupies several tracks, double-click the highest one in the hierarchy).
2. Select Delete objects from the Objects menu (or press Del).
After this, the selected objects should be removed from the scene.
Other times you might need to only remove the rig attached to the character. This is possible as well:
1. As described above, select the entire character by holding Alt and double-clicking the Animation Track that contains the character.
This will select every component that makes up the character.
2. Switch to the Joint Mode.
4. Switch to the Mesh Mode.
5. Repeat step 3.
This will remove every Mesh from the selection.
Now, the only objects that are selected are the parts of the rig.
6. Select Delete objects from the Objects menu (or press Del) to delete them.
After this, all rig elements should be removed from the scene.