* First, Remove Its Battery.
* Remove the Bottom Base Cover Plate
* Removed All Screw Holding the Base Cover
* Proceed Removing All Screws in a Sysmetic Clockwise Order
* Remove All Screws and Aside It on a Piece of Tissue Paper
* View of the D40 DSLR Base With Cover Removed.
* The Gear Operating the Shutter
* Lightly Move the Gear & Inspect for Contamination
* A Closer View of the Gear Seen Through a Magnifying Glass
* Repeat About 5 Cycles.
* Apply New Grease Between Gears
* Spray a Little at a Time & Move Th Gears
* Move the Gears 5 Cycles to Spread Out Grease
* Insert Battery & Test Before Closing Up Cover.
* Close Back Base Cover & Have Fun!
If you want to watch all these instruction with images then open [https://guideusermanual.com/product-name-d40-manual&po=4381&lang=English|Nikon D40 Manual.]