I need free up space in my Mac Air Looking at "about my Mac" it looks I have 40GB as backup but I can not find with ODS

I need free up space in my Mac Air

I used "about my Mac" and it-s telling me I have 40GB as backup but I can not find with ODS (OmniDiskSweeper)

ODS is telling me i have just 30 - 40 GB occupied.

I can find a way to free up the backup file?

I m also using TimeCapsule and the back up there it's just 30 -40 GB (as ODS is finding)

appreciate help