[Zope] Upgrading 2.0 to 2.3

I have a site running on 2.0.1. I would like to upgrade to 2.3.x. I have searched for a how-to on upgrading, but I can't find it. I have not been reading the list closely lately, but I did see a comment about exporting products from the old installation and then importing them to the new installation. Is there anything that has to be done with Data.fs? Should I export the top level folders and objects and import them into the new installation as well? A pointer to a step by step guide would be greatly appreciated. Al