When putting a ball up hill you should remember the following two points!
1. Because the putt is going up a hill the ball will stop rolling faster than normal. Therefore you should not be afraid to hit a nice firm putt. Even if you miss the putt the ball will stop rolling more abruptly than normal and this will reduce the distance the ball roles past the hole.
2. Putts which are hit more firmly than normal will not break as much. While putting up hill, aim with less break than you would with the same putt on a flat surface and make sure you HIT IT FIRM.