To remove the cooling fan and controller, make sure you use an Allen key and screwdriver that fits properly as the countersunk bolts/screws can often be very tight to undo.
I prefer to use hex drive bits like the one shown here:
If the bolts/screws are really tight, and you feel that you may strip the head of the bolt, you can insert the bit and then hammer directly on the end of it, and the shock of the hammer blows should encourage the bolts/screws to loosen.
Some cheap Allen keys can be made from very poor quality steel and they may damage the hexagon head on the inside of the bolt head if it is forced too much and the key slips.
Also make a note of the phase wire positions on the old controller so that you can put them back in the same position on the new controller.
If the new controller has not been set to the correct battery voltage by the supplier, you may need to adjust it using the USB programming lead or Bluetooth dongle before the motor will run.
I apply a small amount of Silicone sealant
(or just smear some Vaseline petroleum jelly) around the flange of the controller to help prevent water getting in.
I also grease
(or Vaseline) the threads of the steel bolts to prevent them from seizing into the Aluminium hub.
Alan