How do I replace main valve for house supply line ?

Depends on where you live whether your allowed. Most houses have 3 ways to stop the water. The curb stop, valve before meter and one after.

The "curb stop" is not your responsibility. This is where the utility's reposbibility ends.

Some jurisdictions may require a licensed plumber to operate the curb stop. Some may require the city to operate the valve. County homeowners where I am at can pick up the tools with a deposit to turn the water on and off at the street.

A nearby city now requires the city to turn on and off the valve. They used to require a licensed plumber. The main valves inside the house cannot be replaced by the homeowner.

KISS covered this quite well, all you need is to tell us which valve you want to replace.