How to reset cisco router to factory default

Follow the following steps if you are already logged in

• go to global configuration mode and enter the following commands
• config-register 0x2142
• reload

System configuration has been modified. Save? [yes/no]:n
Proceed with reload? [confirm]y

now after rebooting change config-register value to 
0x2102 now save the configuration and reboot

If you have forget password connect to the router using console
and start router press CTRL+BREAK
go to rommon mode type config-register 0x2142  and reset
After rebooting router change the config-register value to 0x2102