If you don't like the entire account (FusionFall and Cartoon Network) then you could simply just give it to a sibling or whoever and then just make a new one.
Not sure what to suggest.
If you would rather keep your account but delete one of the characters from the 4 character slots, click the character you want to get rid of and then click delete, type in the name of that character when prompted. (Case sensitive.)
"Sometimes you gotta run before you can walk." - Tony Stark, Iron Man.