$> sudo sed -i 's/gutsy/hardy' /etc/apt/sources.list
$> sudo apt-get update
$> sudo apt-get dist-upgrade

Just done mine, but haven't rebooted yet.

As pointed out in #linode, 'sudo do-release-upgrade' works much more smoothly.

Just for the sake of completeness, do-release-update requires the update-manager-core package installed on your system.

if you do go this route, it's generally a good idea to split the "dist-upgrade" up a slight bit (from experience)

apt-get install apt dpkg libc6

first, *then* dist-upgrade.

Sometimes changes in apt between releases can cause trouble if new packages take advantage of those changes. your dependancies could end up weird.[/code]