Within the app editing section (App Dashboard or Design page) locate the app name on the top left of the page. Click on the pencil (Edit) icon to edit the app name:
Edit your app name and click to save changes, or click to cancel.
Once you click outside the text box the title will be verified and then saved.
App name should be unique within your user account. If you enter a name that is already in use, it will prompt with error message "App name is not available".