To do this we’ll need to open a terminal, to do this I recommend to hit WindowsKey+R and write cmd and hit intro.

After this trivial step we’ll need to see our interfaces and their MTU:
netsh interface ipv4 show subinterfaces

To know the max size we can assign to our MTU we can try with:
ping www.REFERENCEWEB.com -f -l SIZE

And finally to set the MTU that we need we can execute:
netsh interface ipv4 set subinterface "YOUR INTERFACE NAME" mtu=SIZE store=persistent

Discovered via http://www.richard-slater.co.uk/archives/2009/10/23/change-your-mtu-under-vista-or-windows-7/