If we have access to config mode we may type
config t configure factory-default
ciscoasa(config)# config factory-default Based on the management IP address and mask, the DHCP address pool size is reduced to 253 from the platform limit 256 WARNING: The boot system configuration will be cleared. The first image found in disk0:/ will be used to boot the system on the next reload. Verify there is a valid image on disk0:/ or the system will not boot. Begin to apply factory-default configuration: Clear all configuration WARNING: DHCPD bindings cleared on interface 'management', address pool removed Executing command: interface management0/0 Executing command: nameif management INFO: Security level for "management" set to 0 by default. Executing command: ip address 192.168.1.1 255.255.255.0 Executing command: security-level 100 Executing command: no shutdown Executing command: exit Executing command: http server enable Executing command: http 192.168.1.0 255.255.255.0 management Executing command: dhcpd address 192.168.1.2-192.168.1.254 management Executing command: dhcpd enable management Executing command: logging asdm informational Factory-default configuration is completed ciscoasa(config)#
that's all, ASA will remove configuration and we may start to work