I am using WSL 1. My WSL Ubuntu 18.04 rootfs (C:/Users/USERNAME/AppData/Local/Packages/CanonicalGroupLimited.UbuntuonWindows.../LocalState/rootfs/) size on my C: drive is very large due to duplicated data from a mounted disk drive (M:). I would like to remove the duplicated data without affecting the data that is on my M: drive and without adversely affecting my WSL setup. Ideally, I would also like to avoid duplicating the data to my C: drive in the future so I don't put the extra stress on the SSD.
I have tried to unmount the drive from within WSL using sudo umount /mnt/m, but it did not reduce the size of the rootfs on my C: drive. I am afraid of just deleting the data because it is highly recommended not to modify anything within that rootfs from Windows, and I don't want to mess up the WSL image or the data on my M: drive.