Go here to download the new version or use the update manager to upgrade. Make sure you do all the updates on your current version of Kubuntu or Ubuntu first. This goed for 8.04 & 9.04 LTS releases and any other release in between.
In the past updates like this could cause problems when doing them right at the time of release. It was common to find unreachable Ubuntu servers when upgrading causing an update to not work at all, or to just download some of the files and install a broken version of Kubuntu.
This seems to be resolved when I started the upgrade no time outs to Ubuntu servers were reported. Although the upgrade is downloading slow even on a fast broadband connection.
The only thing I now have to worry about is will everything work like it did after the upgrade.
I also have a few servers to upgrade which is usually what the LTS(Long Term Support) version is used for. As well as a few clients who are also on the LTS version.
Keep an eye on this blog for my report on how Kubuntu 10.04 LTS is working after the upgrade.