This question has been answered by andytough. See the first response.
It sound like your config file might be missing: /manager/includes/config.inc.php
Make sure your original config.inc.php file is there, and that it is 'writable' (644). Ensure that permissions are set back to 400 or 404 after the upgrade.
You could try removing the port number :3306 as this Bluehost documentation does not make mention of it being necessary. https://my.bluehost.com/cgi/help/2222. But if it worked before with a port number specified in version 1.1 I would have thought it would work OK with the upgrade.
I have just noticed this in the Bluehost doc.
Database name = (cpanelUsername_databaseName)
Database username = (cpanelUsername_databaseUsername)
This suggests that you should be using a combination of your cpanel name and database name or database user name with an underscore between them. But again, if the config file was working OK before I can't see why you would need to change it now.
What version of MODX Evo are you running?
It may be that an interim version upgrade is required if it is an older version.
If you are being prompted to enter user names and passwords it sounds to me as if the config file is not being read by the installer, or the version you are running is not upgradable.
If the "Upgrade Existing Install" button does not work then I think the only other option is to do a complete/new install? You should not attempt to do this as, if successful, it would overwrite the existing website.