Good Mornrning from Wetherby UK :-)

On this site Crown Hotel - Harrogate, Conference Venue, Events Venue, Restaurant Facilities the shopping cart is third party but i want to track conversions.

Having watched to many YouTube vids my head is spinning. Can anyone begin to explain how I could do this and if i cant do it recommend a company who specialises in integrating google analytics with third party shopping carts.

Thanks in advance,
David