The sd 4 had issues out of the box but with some adjusting are a decent printer. Some of these issues like semi square circles had nothing to do with the board. Also the have a reputation for being somewhat under powered again nothing to do with the main board and the pots need to be adjusted. This is something you would need to do with ramps. before you tear this machine apart to do a heart tansplant you may wan to take some time to learn how the machine is supposed to work and take some time to tune it. I would hate to see you do a ramps upgrade then go through the work to tune it when you may just be able to tune it in the first place.
If your friend and you expect this to Just print you may have picked the wrong hobby.
That being said ask the right questions and people here can help you. The sd4 is not a bad printer especially at the price you paid.
The ramps board is just one component in the system.
You will need to print tethered.
Soliddoodle 4 stock w glass bed------Folger Tech Prusa 2020 upgraded to and titan /aero extruder mirror bed
FT5 with titan/ E3D Aero------MP mini select w glass bed
MP Utimate maker pro-W bondtech extruder
Marlin/Repetier Host/ Slic3r and Cura