You can view it from monitoring | system status option. This screen shows the status of several software and hardware variables at the time the screen displays. From this screen you can also display the status and statistics for SEP modules, system power supplies, memory, and network interfaces.
One of the screen elements:
RAM Size - The total amount of SDRAM memory installed in the VPN Concentrator. Memory Status is a link to a table that displays information about memory use on the VPN Concentrator; it includes information about block size, with data about used and free blocks, bytes, and percentages.
Refer the below URL for more info:
http://www.cisco.com/en/US/docs/security/vpn3000/vpn3000_47/administration/guide/sysstat.html