Trailer load, screwing up?

Hello, I’m in possession of an Audi 80 B4 Limosine with 90hp, is it possible to increase the trailer load somehow? I don’t know how to do that, only I know that I can pull about 1200kg (trailer braked), but my horse alone is already taking a good 600kg and an average trailer weighs 800-900kg I already have! Well, and the risk of what happens and the insurance is not paid for because of overload I hate to go in! How do I get to an Audi 80 B4 Limosine with 90hp! m higher permissible draught weight? By more PS? I ask for help! Greetings Lady!