Looking for direction for a 6 month tourist visa to the USA..?

.. even though I live in a country that is covered by a 90 day waiver tourist visa, I cannot apply for an extended stay for another 90 days on this visa. What and where is the visa form I do need to fill in for a total of a 6 month/180 day stay? I do not need a work visa at this time as I have funds to cover a 6 month stay. But that's not to say that will not change. I am not currently in the USA.