How do i replace a needle valve and seat?

I was just informed in past thread that I probably need a new needle valve and seat......
How do I go about replacing these in a 1988 stock 250x......
and about how much does it cost??

Thanks Again

Pull the carb and flip it over, pull the float bowl off, there will be a pin that holds your floats in place. Pull that pin and lift your floats very carefully, because your needle valve is hooked to your floats by a little clip. Take a 12 millimeter socket and you can remove the seat. You might have to reset your float level. It should cost around $30.00. From the bottom of the float bowl deck, to the bottom of the float should be 18.5 millimeters.

Hope this helps!