You must do this in the proper order:
I suggest you CLOSE out your email application and then open it.
Then...
Click edit so the emails show up with the circle to the left.
Mark all emails as read. --(THIS STEP IS EASILY FORGOTTEN IN THE PROCESS)
Select the first email by pressing the circle.
Then press and hold the Move at the bottom...DO NOT RELEASE IT!!!
While holding the Move deselect the first email.
Continue to hold the MOVE button for maybe 15 seconds.
Then release the Move Button.
Your top email (on right portion of screen) will turn gray.
Then the right portion will display a "stack" of emails.
If you have a lot of emails you have to wait some time while the process occurs.
Eventually the screen will come up to ask where you want to move them.
Select Trash and all will move there as a batch.
The Trash Folder has an option to Delete All--at the very bottom after your last email.