Changing the Configuration Register Settings :

Step1) Connect a terminal or PC to the router console port. If you need help, see the hardware installation guide for your router

Step2) Configure your terminal or terminal emulation software for 9600 baud (default), 8 data bits, no parity, and 2 stop bits.

Step3) Power on the router.
If you are asked whether you would like to enter the initial dialog, answer no: Would you like to enter the initial dialog? [yes]: no

Step4) After a few seconds, the user EXEC prompt (Router>) appears.
Enter privileged EXEC mode by typing enable and, if prompted, enter your password:
Router> enable Password
Pass : <num>

Step5) To change the configuration register settings, enter the config-register value command, where value is a hexadecimal number preceded by 0x:
(config)# config-register 0xvalue

Step6) Save the configuration changes to NVRAM:
Router# copy run start