It is more than just changing from IPv4 addresses to IPv6 addresses. IPv6 is going to be the Internet Protocol of the future and the Internet cannot continue to grow without the introduction of IPv6. The IANA pool of IPv4 addresses is going to be exhausted some time in 2011. Further Internet growth will have to be covered with IPv6 addresses.
So this does not mean we have to tear down all our IPv4 networks, but if you want to access the whole Internet and not be limited to the IPv4 Internet, you have to use IPv6. Both protocols will coexist for many years.
Hope this answers your question,