You can't, unless you know things about type T (for instance, whatever T is, the set of all unique T must be well-ordered and have an upper bound). So T must at least extend some interface that will provide this information. And if this interface provides this information, why would you need a generic class that does nothing but delegate to the methods defined in this interface?
The mind is a strange and wonderful thing. I'm not sure that it will ever be able to figure itself out, everything else, maybe. From the atom to the universe, everything, except itself.
Let's assume you want to do this as an exercise. I suggest you take a look at java.util.Collections and its min and max methods, and what their generic types are.
(Note: the "Object &" part can be omitted since every single type matches that.)