Unstable reading from pushbutton on digital pin
At the moment, your resistor isn't doing anything useful. When your switch is open, the pin is still 'floating', which means it's ending up with random stray readings from nearby electromagnetic fields.

You basically need two connections coming from your Arduino pin. One goes through a resistor straight to ground. The other goes through your switch straight to +5V.

In that case, the resistor is acting as a pull-down, because it holds your pin at Ground whenever the switch is open. You could swap over the ground and +5V, and it the resistor would function as a pull-up instead.

This question deals with the same kind of issue:


Button state changing randomly