i can't find out how to induvidially control the LEDs.
You have a byte array, one entry for each shift register.
When you want to turn an LED on or off you do a bit set or bit clear on the bit that corresponds to the LED you want to change and then write the whole array out to the shift registers.
Most of the LEDs are getting the same controlling bit as last time and so will not change, only the LED that you did the bit set or clear on will change.