Awhh, well, hey guys! xD Welcome to the forum. c:
To delete characters from an account, all Amethyst needs to do is go into her Character Selection screen, and click 'Edit' for the characters she wants to delete. Then, on the far right tab (where you usually click "Save" for a character), she can click Delete, and that will delete those characters.
However, if you guys wanted to keep those characters for yourselves, you can write down their colors on paper before you delete them, and then remake your characters on your account.
Have fun, you two~ c: