I would start out by wiping down them damp sponging the fan blades top and bottom. If you have a air copressor and don't mind a mess you can use low pressure air to blow thru all the cooling ports on the motor.This is the way I clean ours but it doesn't make my wife very happy. You can also shut off power and disassemble to the point you are comfortable with then brush and vacumn.
I have found that the ones that I have taken completely down,while it does make them easier to clean they have all had sealed bearing motors so not able to lube.Hope this helps you. Thanks.