atmega328p-pu lock bits

i am using arduino uno (atmega328p-pu) and wanted to change the lock bits so that my program is safe from anyone. i know we cant change the lock bits with arduino bootloader. Can anyone tell me how to change the lock bits if we have two arduinos and one arduino can be used as an ISP?

If you setup one arduino with the ArduinoISP sketch, then you can use "upload using programmer" to upload your sketch, and then change the lock bits with avrdude. Note that this erases the bootloader (you can't have the bootloader and locked access at the same time), and you'll have to use "upload using programmer" to burn any additional sketches as well.

Ohh! i see.. u mean i have to write my whole program again and upload it using 'upload using programmer' and then change the lock bits. Well, can you tell me how can we use 1 arduino as a ISP to upload a sketch on the other arduino. I am new to Arduino and need your guidance..

THANK YOU