From a Home screen, tap the Apps icon (located at the bottom).
If unavailable, tap the Dropdown menu (located in the upper-left) then select Alphabetical. If still unavailable, refer to Manage App Icons.
Tap the Check box located to the left of the message(s).
Message(s) marked for deletion when a check mark is present.
To delete all messages, tap the Menu icon (located in the upper-right) then tap Select all. At least 1 message must be selected (checked) to mark all messages for deletion.