the last time I updated, it was from Ubuntu Studio 64 to Mint 6.
From a 64 bit system to a 32 bit?? I don't think that's possible.... (uname -a says it's i686)
And it is not possible to upgrade from Ubuntu to Mint without a lot of work, but to get a mintified Ubuntu is simple
There is no main updater for upgrading versions in the repositories, you may have seen mintUpdate which is the normal tool to keep your system up to date
You can find the upgrade path in the release notes
but in your case a fresh install is recommended