You would upload everything EXCEPT the config files. You would run the required upgrades correct. The documentation in the documentations folder should cover the upgrade procedure.
The error you have is in the 8.0 upgrade we add a new usergroup permission and if you do not run the upgrade you will not be authenticated. That is why you are not an admin.
Like I said if you do all that and still have an error you can try the file edit above to show you the real error but I am pretty darn sure here what your issue is.