Welcome to Android Central! What device? That's usually something that's taken care of on the server side, rather than requiring you to empty the trash. It shouldn't be taking up actual space.
It depends on whether your AOL email service is set up for IMAP or POP3 (on the web site). POP3 keeps the emails on the phone, so you have to delete them from the phone and from any other device you use to access the account. IMAP keeps them on the server, so going to the account on your computer will filter down to the phone, and they won't be shown there either.