backup exec 2010

i do computer work for a nonprofit in my business building am they have asked me to help free up space for backups.  they are currently backing up onto mirrored 2tb extrenals.  i have never used this product before am could use some information on how to free up some space.  also, i would appreciate any general advice for future use and can someone explain what a bkf file is and do i need all of them or is each bkf a seperate instance of a backup.