There's two methods to go for really. Firstly, you can remove the pitch resistor and put wires going to the pot there instead.
The second way is the voltage divider method - here you leave the pitch resistor in, and solder the wires to the pot as before, then solder a wire going from the pot's spare solder lug to ground. You can solder to the battery terminals, or as I prefer, find a ground point on the circuit board and solder to that instead.
The first method, it doesn't matter which way round the wires go to the pot, but it's important with the voltage drop method, as otherwise you get a weird pitch range. Test the connections with a couple of crocodile leads first to see which way round they're meant to go. Then you can fine tune the range with a couple of trimmers on the pot's two outside lugs. The value is not so important with a voltage divider, 100k is usually good though, but experiment if you get an odd range even after swapping the wires over.
I tend to prefer the voltage divider method, as this usually gives a nicer sweep from low to high pitches. Removing the resistor tends to give a logarithmic response where most of the pot is slower speeds, with all the high pitch bunched up at the top. However sometimes this is more pleasing for certain types of instrument - ie, more range in the slow speeds is better for controlling drones
Plus you can always put a fine tune pot on there as well!
