They guys over at Harmonix have posted details on the title update that recently became available. It’s worth noting that you’ll need delete and re-download (for free) a few of the songs if you want to fix a few of the bugs. Read the forum post, it explains what you need to do and why.
Here are the instructions for deleting the content:
Navigate to the System Blade ( purple ), select memory, all devices, games, Rock Band, search for any of the updated songs ( right trigger is a page down 🙂 ), select the song with the A button, and then select Delete
Once you do that, you’ll need to re-download the songs from from marketplace or from the download history (by pressing the guide button, select your gamercard and press A. Go to account management then to download history.)
Edit: If you are in Canada and could not see this content it should now be available for re-download.