Can't delete backup set

Hello,

Norton 360 v21.6.0.32

Is telling me I have low space on back up, please buy more.

My previous back up set was ~3.5GB.

This is now not required. I have reduced the back up set to 300MB.

This smaller set is the set I want to use going forward. I do  not need the other previous large set - at all.

I want to delete the large set.

Norton won't let me because (see picture)

N360 idiocy.PNGI am, apparently, successfully backing up the new smaller set, but I can't delete the old set, and I keep getting the notification that storage is low, please buy more.

These things are not mutually agreeable!

If my back up set is 300MB then I have plenty of the 4.0GB available, not the 173 MB that Norton insists.

Questions: How do I clear out the old, redundant, 3.5GB backup, and only keep the new 300MB one. How do I categorically confirm this has been completed?

Thank you for any help that anyone can provide.

Kind Regards,

InsomniacFolder