You can change it to 2 wheel drive robot. There is two different solution for that.
You can connect just two motor:
-Right one to hMotA or hMorB
-Left one to hMotC or hMotD
It will work fine.
All drive control functions and methods are in [here].(https://github.com/husarion/hFramework/blob/master/src/rosbot/ROSbot.cpp) You will find 4 wheels in this file: FL, FR, RL, RR. You just have to simplify all of them to Left and Right wheels. For example:
wheelFL = new Wheel(hMotD, 1);
wheelRL = new Wheel(hMotC, 1);
wheelFR = new Wheel(hMotA, 0);
wheelRR = new Wheel(hMotB, 0);
Will be looking like this after changes:
wheelL = new Wheel(hMotD, 1);
wheelR = new Wheel(hMotA, 0);
Of course, you don’t have to create your own version of hFramework, you can include this function in your main.cpp with different names.