In order to delete messages using a desktop, you will need to click on the little box to the left of the message and then scroll down to the bottom and click 'delete'. If you would like to delete all of your messages then you will need to click on the little box next to 'Select all' which is above your messages on the left hand side, you will then need to scroll down to the bottom and click 'delete'.
In order to delete messages from your Inbox using a mobile device, you will need to click on the message and then click on the 'X' in the top right corner of the message box. You will then be asked to 'Do you want to delete this message?' Click 'yes, delete' and the message will disappear. If you would like to delete multiple messages at the same time, then you will need to log-in using a computer.