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You will also want to utilize a switch, which looks like this:
Your kit should have come with a couple of them, you will need ONE.
The switch circuit will involve hooking up 3.3v to the center pin, putting a 1k resistor between the pin of the switch and the 3.3v source coming from the pi. And ONE of the other pins should then go through a 10k resistor into a GPIO pin on the pi (set to INPUT mode, just like the buttons).
This switch is going to control the DIRECTION of change- one way, it will be INCREASING in value. The other, it will be DECREASING.