Go to the local computer store or retail outlet and buy a can of compressed air. Take the computer out of it's confined space, unplug it from the wall, keyboard monitor, etc. and take it outside to blow out with the air. Open the case and blow out the case, all fans, including the power supply fan.
All the dust and grease you mentioned can decrease the life of your computer due to heat and if it gets bad enough grease can cause shorting of components and corrosion.
All the dust and grease you mentioned can decrease the life of your computer due to heat and if it gets bad enough grease can cause shorting of components and corrosion.