I and R are not independed quiantites. If you increase R, I will decrease. If you decrease R, I will increse. You have remeber that relation, and then look at the squares. Remember V=IR
So in P = V^2/R if R increases the I will decrease if V stays constant
So in P=I^2R Even though R is increasing I will be decreasing more rapidly because it is squared leading to a drop in power in both equations.