When you are in your mail account, there are Icons at the top the the window. Tap your inbox and on the left hand side where your mail messages are listed, the word Edit is at the top. Tap it and you can select emails that you want to delete. The word Delete should be at the bottom of that window in red. Select the message by tapping the circle next to the message and a red checkmark appears. The delete icon at the bottom of the window is now "active". Tap delete and it will remove the message.
Another way to delete messages is to swipe across the message in the list and a red Delete box pops up or as stated above, tap the trash icon in the open email that you are currently reading.
Depending upon which folder you are in - for instance the Trash folder - you may have the option to delete all messages at once.
Message was edited by: Demo