Who pays investor rating services like JP Morgan to upgrade or downgrade a particular stock or company?

It would follow that whomever pays these rating's services has something to gain from their services as they are the customer of those services. If a stock is going to be upgraded or downgraded, people in the know can profit from that prior knowledge as it were. So how is the playing field levelled for that information? Can an individual like me find out that info at the same time as the major investor players?

They aren't paid to upgrade or downgrade. They are paid to report the grade.

It is offered as a service to their investors -- and is usually paid for indirectly through trading fees. In the past, research has always been bundled with other products. There are some investment funds (e.g., Fidelity) that have negotiated lower trading costs and pay for research directly.

I don't believe that anyone directly pays to have a company upgraded or downgraded by an investment bank's researchers. The researches do it as a free service for the bank's clients. The hope is that the research will make the clients want to do something (like buy or sell a stock) and that the client will most likely do the buying or selling through that investment bank. The banks make a small comission on all deals done by their clients.

I think if you become a client of one of those investment banks you can get access to their research. There are also other services (like on bloomberg) that collate a large number of different companies research but I've never used them so I have no specific advice for you on that part.