The simple answer is that you can't.
Tractors are fundamentally top-heavy and unstable on anything but flat, even ground.
Unfortunately, almost no one has flat, even ground to take care of, so a certain amount of careful hillside negotiation is usually required of any tractor operator. What you can do is learn how to operate your tractor less unsafely when hillside use is unavoidable. Here are some tips, accessories and warnings for preparing tractors for and operating them on uneven ground. If it feels dangerous, it probably is. It doesn't need to feel dangerous to be dangerous.