Cisco seems to have removed the Administration Guides from the support page for this end-of-sale product. I notice my local copies are about 4 years old (and the product was considered obsolete even then).
The procedure for resetting to default is listed in the FAQ page which is still available. You can also recover password using the procedure listed there if you need it.
Most VPN 3000 administration is done via the Web UI but you can go through seup from the command line as well. Typical procedure is to use console / command line for basic setup (system address, gateway etc.) and then move to the Web UI for completing and modifying from there.