Basically, if you can get to network and sharing center, if that still exists in 8, there should be some area saying "change adapter settings" or something to that effect. If you click that, you should be taken to an area that shows your local area connection, your wireless connection, bluetooth if you have that enabled, etc. If you right click on the wireless connection and choose "properties", you'll have a box that pops up where you can untick IPv6.
Edit: Just realized you said you can uncheck. Just uncheck. You're at the right place, as there's only one place.
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