Using 55" LED (LG 55lh90) as monitor but it only recognizes 60hz refresh rate.?

I bought the tv because it boasts 240hz refresh rate and I'm extremely interested in purchasing Nvidia's 3d vision kit however, when I go to my display settings it only allows me to select up to 60hz. I have the tv hooked up through HDMI into my Nvidia GTX 260.
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