NBU appliance upgrade

Hi Folks,

I have a NBU appliance 5220 , at version and disk space :

Appliance Version: 2.5.3
NetBackup Version: 7.5.0.6
Build Date: 20130628

UKDC1:/home/maintenance # df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             229G  170G   48G  79% /
udev                   24G  420K   24G   1% /dev
/dev/sda3             656G   38G  585G   7% /log
tmpfs                 4.0K     0  4.0K   0% /dev/vx
/dev/vx/dsk/nbuapp/pdvol
                       40T   34T  6.3T  85% /disk
/dev/vx/dsk/nbuapp/catvol
                      1.0G  551M  444M  56% /cat

I want to know how much free disk space is required to upgrade it to 2.6 version