Tutorial: Reading Water Flow rate with Water Flow Sensor

HEY

I have bought a G1/2 Water Flow sensor . But it gives an output for only upto 3 lpm .

What changes do i have to make to this sensor so that it can measure upto 6 or 7 lpm.

Do i use a more sensitive hall effect sensors so that it is able to capture the faster rotations of the rotor. Could you please suggest a hall effect sensor .

REPLY ASAP PLEASE.