A 7-segment digit has 7 segments (often also a 'dot') and a common line. Assuming you are tying the common line to one of the power rails, and each segment A to G is connected to one I/O line at the Arduino, then the likely problem is that your new display requires more current than the small display required. That's not shocking at all. It's also possible, since you don't say, that the newer display uses a different color LED segment. Red requires the least voltage, blue the most. So that can also matter. (There are other differences -- ultra high efficiency LEDs vs standard efficiency, for example.)
Keeping the large display, take one of your 1k? resistors and replace it with a smaller value. Try 450?, for example. Make it still smaller if that isn't bright enough, larger if it seems too bright (which I doubt will happen.) Keep up the adjustment of just this one resistor until you get a segment that is about right. If you have a volt meter, measure the voltage across this resistor. Then divide that voltage by the resistance. If the value is more than 0.010 (10mA) or so, then you may be working the Uno I/O port too much and may need to consider transistors externally or else risk the micro if all 7 segments need to be lit. And if all this pans out okay, change out the other resistors and see how it goes.
EDIT: Try out 220? then. I think that would be approximately the right value for limiting current from a 5V supply.
I have a simple Arduino Uno running a small 7-segment display using a separate pin output for each segment under a 1K resistance and 5 v output.
I want to run a larger 56mm x 38 mm 7 segment display but when I plugged it in, it barely lit up and it is very dim.
Should I lower the resistance (if so to what) or get rid of the resistors all together?
