How to delete large commits

Hi,

I have accidentally pushed several folders containing large numbers of files to a repo. This is eating up a large amount of space on the repo. I would like to delete these commits so that the space is freed. How do I delete commits from gitlab.com? Thanks for your help!

-Jack

p.s. I have included an image showing the recent commits on my account. I would like to delete the three commits from Aug 29, and return the repo to the state it was in on Aug 26 so that the memory consumed by the repo is at the level it was on Aug 26.