Hi Ramesh
all you have to do it to add another harddisk using your vsphere (or vcenter i mean, and if you have Vmware admin in your environment, you should consult him/her) with size of 8 GB to your PAM appliance , then you have to reboot the system, it will detect the new harddisk and map it (ex: it will be a s /dev/sd1)
anyway the upgrade process will detect it while upgrading.
best regards