To delete the particular snapshot(s) from your existing backup store, Please use the “Regen Backup Store Groom Tool” which can be downloaded from the following URL:
http://www.techsupportlive.com/index.php?_m=downloads&_a=viewdownload&downloaditemid=56
To know more about Regen Backup store groom tool please refer to the document available in the following URL:
http://www.techsupportlive.com/index.php?_m=downloads&_a=viewdownload&downloaditemid=58