You either get the unlock code from the carrier it's currently on (and it has to be on an active account) or you buy it from an unlock code seller on eBay. Each individual phone has a different unlock code, so no one here can help you with yours.
Some carriers will give you the code, some will give it to you if you're traveling out of the country, some will sell it to you and some just won't give it to you at all.