I suggest just using alcohol wipes to clean the exterior and a high pressure air compressor (gun) to blow thru ventilation grills/openings. Hopefully this will spin the fans fast enough to clear the dust on them too. You could see if there are quick access covers that can be removed without tools to open them and clean what you can access.
If the storage unit is HDD, you could also replace it with a regular SSD for a good price. This makes a ground and sky difference in performance.