how to manage bound volumes

Hi all
New to and enjoying a lot
I have deployed a Strapi app and its working fine, but somehow I have 2 x 40G volumes running which I didn’t intend to have . I am sure that the 3g volume will be fine . When I try to delete them the fly volumes api says they are bound to the 2 machines that I have on the db app.
I did not create these machines intentionally either… are they integral to my postgres db app or not?
Basically how do I minimize costs in this situation?
Thanks for any help!
Ben Amato