So in essence you would follow the upgrade guide
https://www.ubbcentral.com/doc_upgrade7.phpWithout the need to upload the install folder and contents nor the need to run upgrade as long as you upload the same version you download from the members area.
Also do not forget to make a backup before you start in case you overwrite files you should not have.
Currently you have a connection issue "Problem occurred in connection".
If reuploading the stock files does not resolve the issue I would check
includes/config.inc.php
This holds the login info for your database as well as other parameters.
