Upgrading from 4.6 to 5.5.3 - [Error: Remove Moneris] CiviCRM_API3_Exception: "Could not delete payment processor type"
This error relates to the fact that there used to be payment processor code in CiviCRM core to support the Moneris payment processor.  If you don't interact with Moneris, this is fairly safe to ignore.  However, I suspect the error may mean you use Moneris, in which case I would NOT follow the instructions below.


In your CiviCRM folder, find the file located at CRM/Upgrade/Incremental/php/FourSeven.php. 
Delete line 193.  Confirm it matches the line 193 linked here.
Run the upgrade again.


Note that it's common to experience upgrade errors because you have a partially upgraded database - so be sure to restore the pre-upgrade database backup to minimize your upgrade pain.