If you no longer require a file for any part of your site you can delete it from the file gallery and free up storage space.
Scroll down to the Create your website section and click on the Website Builder icon.
Click on the Login button next to the relevant package.
In the design view main window select the file you wish to delete. Click the X button
To finalise deletion from the File gallery click the Delete button.
Please note: If you simply delete the file from the File Gallery and you have already placed the file within your site, that file will remain viewable in those pages unless you remove it from those pages.