Hi D'nelle! Great question. When logged in to your account there is a way to view your image library without having to first create or open a mailing.
To do that, click Campaigns at the top of the page then near the upper right corner you will see the Images and Documents buttons.
Once your image library is open, you can upload additional images one at a time or use the menu icon to the far right of the image to delete images one at a time. A mass import or cleanup option is not yet being developed but is something we have discussed with our product team.
Additional details on how the image and document libraries work can be found here.