How to restore default configuration of Cisco PIX 501 firewall

I am currently on Cisco PIX 501 firewall. It was initially configured by a network engineer who left our office. I want to make changes in it but I am unable to save any changes. How do I restore it to factory defaults? I know I need to reconfigure the firewall once and it would be tedious but I am ready to do, I just need the steps or tips to restore it to factory settings as it came before during purchase. Can you help me to get my work done?

Step 1:- Log in to the PIX Firewall. (If you forgot the Cisco PIX 501 firewall password, just refer this guide Password Recovery Procedure)
Step 2:- Once logged in, enter the global configuration mode and issue one of these commands:

clear config all
write erase

Step 3:- Reload the PIX Firewall.

All you need is the "PDM" or Pix Device Manager of Cisco. It helps you to restore the firewall to its factory default settings. Pix Device Manager runs using a web browser. Just go to Pix Device Manager and click on "File" and then select "Reset PIX to Factory Default Configuration". That's it.

Try using a terminal emulation program (TELNET) and enter the following commands:

Step 1: configure factory-default [inside ip address [address_mask]]
Step 2: write memory

Description

The first step erases the running configuration and replaces it with the factory default configuration. The second step writes the factory default configuration to Flash memory.