To edit an existing app, click on Apps & Sites located on the left-hand menu:
Move your mouse to hover over the application you wish to edit. The application will be highlighted in gray, and a small menu will appear on the right-hand side. Click on the pen icon to edit your application (see below).
You will now be able to edit your App Name in the text box.
After you have completed all the changes, click the checkmark icon on the right-hand side to update & save the changes. If you wish to cancel your edit, click the X icon.