To change the value of the internal pull-up resistors you should go to the following directory:
In there you will find, among others settings, the option to change the pull-up resistor value. For example, to change the value of the pull-up resistor for the GPIO49, which is the IO8 in the Arduino Expansion Board, you have to use the following commands:
cd /sys/kernel/debug/gpio_debug/gpio49 echo "2k" > current_pullstrength
You can check what the available values are with the following command:
cd /sys/kernel/debug/gpio_debug/gpio49 cat available_pullstrength
I hope you find this information useful. There are more settings that you can check. I think you will find them interesting.