smarq8:
I theory UNO and NANO are same uC so is it safe to programmin my NANO as UNO?
Absolutely. I do this with all my Nanos. It also frees up 1.5 kB of program memory and allows you to use the watchdog timer to reset the microcontroller. For most beginners it's not worth adding the complexity of burning the bootloader but it's definitely worth the effort for anyone at a more advanced stage with Arduino.