You don't need to change much - if everything's working at the moment (albeit dimly), just do the following:
- buffer each of the 4511 outputs with a single NPN (e.g. bc547): 4511 output to NPN base, VCC to NPN collector; the NPN emitter is the new buffered output.
- reduce the resistors to the LED anodes. For VCC=5V, the resistor voltage is 5-Vled-.7=2.3, so for 20mA average (for 10LEDs), use R = 12ohms. This gives a peak current of 200mA per LED, so make sure this is within the manufacturer's specs.
I see there is no series resistor to the base of the digit CC transistors: you should have limiting resistors there also.