Real handy KB article (KB929852) on How to disable IP version 6 or its specific components in Windows that provides automated Microsoft fixits to enable or disable IPV6, as well as manually instructions

enable or disable IP version 6 or its specific components in Windows

howeveer please note

We do not recommend disabling IPv6. However, if you must disable IPv6 or components of IPv6, follow the steps in this article. For more information about why we do not recommend disabling IPv6, see the "What are Microsoft's recommendations about disabling IPv6?" question in the following article: 

IPv6 for Microsoft Windows: Frequently Asked Questions

Rob