1. Check this link and follow up and if not clear… and check below comment on this page
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_password_recovery09186a008009478b.shtml
2. Need to verify version to download proper file of "PIX Password Lockout Utility".
ex) In this case version 6.3
3. Go to the below site and pick right file to download.
ex) file name np63.bin
4. Reboot PIX501 and push ‘Break’ or ‘EST’ bottun to get
5. Assign IP address
– Choose interface
– Configure IP address
– Configure Gateway IP
– Configure TFTP IP
– Configure file
– Ping testing
6. Upload the file and reboot
Reference : www.cisco.com