IPv6 on Windows is enabled by default and is really suggested to do not disable it if you don’t have a good reason. Disabling completely IPv6 can introduce some boot delay around 5 second; but if you still want to do that: https://support.microsoft.com/en-us/kb/929852
If you simply do not manage/route the IPv6 traffic on your network, or better you are running on an IPv6 only network, can be useful to disable the unused IPv6 transition protocols.
On Windows 8 clients using PowerShell, open an elevated PowerShell prompt and execute the following commands:
Set-Net6to4Configuration –State disabled Set-NetTeredoConfiguration –Type disabled Set-NetIsatapConfiguration –State disabled
On Windows 7 client using netsh, open an elevated command prompt and execute the following commands:
netsh interface 6to4 set state disabled netsh interface teredo set state disabled netsh interface isatap set state disabled
To learn more about IPv6 check this blog: http://blogs.technet.com/b/askpfeplat/archive/2013/06/24/ipv6-for-the-windows-administrator-ipv6-fundamentals.aspx