delete storage on onedrive

OneDrive is on the cloud and also on your computer.  What you do in one place in OneDrive is reflected in all the other places in OneDrive.  Your Documents, Desktop, and Pictures folders are part of OneDrive unless you turn off the syncing of these folders in Manage Backup.

However, to play it safe, keeping files on a drive other than the C: drive will ensure that they can never sync to OneDrive.