If they are all in one folder then set your Explorer to show the file details and make sure you have 'Date Modified' as one of the criteria. Then list by file type.
The BPN files will be in date order - delete what you need.
Or if they are in folders within folders then in the parent folder search for all BPN files. Again you need the results to sow a 'detail' list with 'DateModified'
Date modified can be different to just 'Date'or 'Date Created' so youneed when the files was last modified.
Another option (which I would not advise) is in the Work Environment > Data Safety And Integrity you can turn off the backups completely.
But then you lose a safety net if something happens to you main file or you need to go back one save.
There is only one BPN per job file and personally I would keep it as a safety net.
Get an second hard drive and archive older file there.
Also remember to empty your recycle bin when you delete files other wise you haven't really removed them from your hard drive at all.
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