First ensure that your firmware is updated to the last version (Management > system management > firmware upgrade). It should be 1.04. If not upgarde first (ftp://ftp.dlink.eu/Products/dns/dns-320l/driver_software/DNS-320L_fw_revA_1-04b08_all_en_20140822.zip)
Then you just download the files that are in this board and go to Management > Application Managamenent > Add-ons