Automatic migration?

always always always make at least two full backups before installing a major release.

If you do an upgrade install, your data will not be disturbed. Data does not need to be migrated - the OS is what gets changed.

again make at least two backups. and always have a backup anyway. the forums get so many threads from people who did not have backups and somehow things got screwed up and they are desperately trying to recover their important photos, documents, music, financial information (the legal info, not the bribes and such), application settings (like bookmarks), mail stuff, and secret plans to take over the world.