There are no special requirements if you are upgrading from any version later than 3.0.0. but you are likely to find initially that you have no menus displayed. To fix this login (if necessary set your browser URL to your-domain/login.php to do this), and visit the administration pages. Just visiting there is sufficient to complete the upgrade process and allow the menus to display normally again.
Another dane and I had the issue with one of my installations too. Even if we setup the login we can not access the page. Since we did not knew the cause of the problem – we just /del all beside /data folder! So I think we just might to /delete the calender folder.
admin and owner of a user customized version of kiwitrees (contains 3 family trees)