Hi, I work for a Sage BP and can confirm that you do need to have Sage 200 delivered through a partner rather than direct from Sage. This is because Sage 200 should be tailored to suit your business, have your Sage 50 data migrated (quite often with changes to things like nominal structures) and fully trained on for you to gain the full benefit of product.
mdenis90 asks a very good question though. Why do you need to upgrade? Really there should be some very good reasons such as Speed, Stock management, multi tier nominal requirement etc. Sometimes various 3rd party add-ons can be a better option both functionality and commercially.
Feel free to ask any questions you may have.