In circuits like this, where you are driving a bunch of LEDs as a unit, I have found that you don't need a dedicated resistor for each LED. For example, in the schematic given, you can calculate the equivalent resistance of all four 330-ohm resistors in parallel, which is 330/4 = 82.5 ohms. So find a single resistor in the 80 to 90 ohm range, wire one side to the Arduino +5V, the other side to all the positive LED terminals connected together, and the rest of the circuit remains the same.
This works because the four resistors in the given schematic have, in theory, identical current flowing through them, and therefore identical voltage drop across them, so it is as if the bottom of all the resistors are connected, due to the voltage at the bottom of each being identical. If they were connected, you would have four resistors in parallel, hence the 330/4 formula above.
Note that this does NOT work if you are trying to turn on/off LEDs independently of each other; in that case, each LED must have an independent resistor in order to safely limit the current flowing through the LED. This trick also assumes that all the LEDs are the same kind, and all are connected to the same transistor driver, so that the assumption of identical current flowing through all resistors is identical.