You don't exactly "upgrade" it; you can configure your computer for IPv6, but continue using IPv4 for a while. Not many servers exist yet for IPv6; if you want to access an IPv4 server, you need to use IPv4 on your side, as well. To use IPv6 on your end, you need to access a server that also works with IPv6.
So, basically, you need to:
- Ask your ISP (Internet Service Provider) whether they have support for IPv6.
- Ask the ISP how you should configure your computer to work with IPv6. (I am not sure whether there is a standard method that works in most cases - perhaps you just enable it.)
- Configure your computer.
- Look around for Web sites that use IPv6. For a start, I believe there is an ipv6.google.com, which you can use for testing your connectivity.