Wordpress Worldpay Payment Integration adjustment - already installed

I recently had a new website developed on Wordpress. A custom key feature I have is WorldPay gateway payment integration, this was installed using custom CSS and API keys. My order form and test payments work completely fine.

The API keys installed were test keys to allow test transactions. However my website is now live for customers and i now have the new live activated API keys which need to replace the previous API test keys. My developer has disappeared and I need this change made ASAP as customers are trying to make purchases but the payment page is still in test mode because of the API test keys.

I also need the following added in addition to the API keys exchange:

- swap API test key codes with API live activated key codes
- a discount code featured added to my order form page just before checkout
- some details on the WorldPay checkout page need to be fine tuned as some information passed through is distorted
- set up a Payment Response URL in order for customer and admin tp receive the transaction/order form summary information via email

I need this all done ASAP today. Prompt communication in clear English is a must. Budget is also fixed.