Prepare for your upgrade
Check your server is set-up correctly
Post any upgrade script errors problems in the forums
After upgrade, clear any cookies in your browser to avoid getting token errors.
Load the admin page & press Ctrl+F5 twice to force the browser to update the css changes.
Goto Admin -> Users -> User Groups and Edit the Top Adminstrator group. Check All boxes.
Goto Admin and Edit the main System Settings. Update all fields and click save, even if nothing changed.
Load the store front & press Ctrl+F5 twice to force the browser to update the css changes.