If you have lost the administrator password to access the security appliance you can recover the ASA password with the following steps:
Recovering your Password on Cisco ASA
Step1: Connect to the firewall using a console cable
Step2: Power cycle the appliance (power off and then on)
Step3: Press the Escape key to enter ROMMON mode
Step4: Use confreg command to change the configuration register to 0x41
rommon #1> confreg 0x41
Step5: Configure the security appliance to ignore the startup configuration.
rommon #2> confreg
The ASA firewall will display the current configuration register value and boot parameters and ask you if you want to change them
Current Configuration Register: 0x00000041
Configuration Summary:
boot default image from Flash
ignore system configuration
Do you wish to change this configuration? y/n [n]: y
Step6: At the prompt enter Y to change the parameters.
Step7: Accept the default values for all settings (at the prompt enter Y)
Step8: Reload the ASA appliance by entering the following command
rommon #3> boot
The firewall will reboot and load the default configuration instead of the startup configuration.
Step9: Enter into EXEC mode
hostname> enable
When prompted for the password, press Enter (the password in blank now)
Step 10: Access the global configuration mode and change the passwords as required:
hostname# configure terminal
hostname(config)# password password
hostname(config)# enable password password
hostname(config)# username name password password
Step 11: Load the default configuration register value (0x1) by entering the following command:
hostname(config)# no config-register
Step 12: Save the new passwords to the startup configuration by entering the following command:
hostname(config)# copy running-config startup-config
The above works for all ASA models such as 5505, 5510, 5520 etc