Please try the advice given in this prior Q&A (also includes Martin's advice for log in/out): https://biostar.usegalaxy.org/p/25136/#25145
But log in/out will not completely solve your issue. I see active large histories plus a few that are deleted but not permanently deleted at https://usegalaxy.org. Follow the linked help in the other post for how to find these.
Thanks! Jen, Galaxy team