Multiplexed LEDs are dim

Using Arduino LEDs and Multiplexing
1

I have a spark fun Mux breakout which is a shift register. I Multiplexed LEDs and made them cycle really fast so I can control them individually they are dim though. How can I fix this? Do I increase voltage? Do I give it the LED less resistance? What should I do?

2

arduinoPi:
I have a spark fun Mux breakout which is a shift register. I Multiplexed LEDs and made them cycle really fast so I can control them individually they are dim though. How can I fix this? Do I increase voltage? Do I give it the LED less resistance? What should I do?

Which "Mux breakout"? More voltage than what? Less resistance than what? What values are you using at the moment? What's your multiplexing ratio? What's the maximum pulse current of your LEDs?