Resistors R4-10 are important to regulate the current to the LED segments. The value depends on the voltage supply you are using. The value can be calculated using Ohms Law.
R = V / I
or in this case
Resistor = ( Supply Voltage - Vf ) / If
Assuming that you are using a standard display requiring a current ( If ) of 20mA per segment and the LEDs have a forward voltage ( Vf ) of about 2.5volts then then with a 9 volt supply the value is
Resistor = ( 9 - 2.5 ) / 0.02 = 325 ohms (or 330 ohms).
A good rule of thumb is to use 330 ohm resistors anyway.
This will still keep the current within the tolerance of most displays.