That's quite a bit different!

They're not using the onboard stepper drivers, so there's not really any point in keeping any of the existing motion controller boards. You just need to find a manual for the three stepper drivers that are fitted.
The biggest thing you'll need to work out is the wiring for the relay board in the centre.

Is the existing controller using USB? If so, does it still work, or do you not have the required software?