The more messages you receive, the more you'll likely need to delete messages to keep your Inbox folder from overflowing with too many messages. To delete messages, you can delete them individually or select multiple messages and delete them all at once.
To delete a message, follow these steps:
Follow all the steps in Reading Email in What You'll Be Using to view the message you want to delete.
Tap Trash at the top of the screen. The currently displayed message gets moved to the Trash folder.