Go to Configuration > Payment and Shipping Gateways and click to edit QuickPay.
For the 'friendly name', enter the name you want this payment system to be referred to on the front of your site where customers select it, for example 'Pay by credit card with QuickPay'.
ProcessCurrency - If your QuickPay account can process orders in all the currencies you have available for customers to use on the site, then you can leave this blank to process the order in whatever currency the customer is using. If you cannot process all the currencies available, you can convert all orders to a specified currency at checkout. The total will be shown to the user in both currencies, with an explanation. For example, setting this to 'GBP' will convert all orders to British Pounds at checkout.
PostURL should be set to https://payment.quickpay.net
Version should be left as defaulted (most likely v10)
Change the Status from 'OFF' to 'ON' (for live orders) or 'TEST' or 'FAKE' for testing. 'TEST' means that a test order will be passed, allowing you to test the full integration and pass multiple orders and no cost without needed to do refunds. 'FAKE' means that Kartris will skip the QuickPay payment process and instead format a post back itself to the callback page of Kartris. This is useful for testing that the callback process works, triggers the appropriate emails and so on without keep having to keep going through the QuickPay test payment process.
MerchantID should be the setting for this field you obtained from QuickPay in @17.17.1.1. Merchant ID