Hi,
You will have to use the console connection.
If you know the passwords and can log on to the device then you could simply erase the configuration with "write erase" command. Be carefull that you dont actually erase the flash.
If you dont know the password to the device then you would have to perform password recovery to get access to the device and do the above.
There is also an "factory-default" type command but I have never had the need to use it. I just wipe the whole configuration clean before starting a new configuration.
Heres a document on the Password Recovery.
http://www.cisco.com/en/US/docs/security/asa/asa72/configuration/guide/trouble.html#wp1049302
Its for a bit older software but I imagine it hasnt changed much
- Jouni
