As @Farzad-Cyrus mentioned, an icon displaying an arrow pointing down to a solid, horizontal line would generally indicate an automatic scroll function- it's pointing to the bottom-most line and this would suggest that action. Similarly, the arrow into an open box gives a strong indication that the item in question must be downloaded. I wonder if it is obvious enough to explain that it is a software update and a download will trigger an automatic install, none of which the user will experience. This icon is often seen on document downloads and image downloads, resulting in something (comparatively) tangible for the user to interact with.
Alternatively, you could go down the route of trying to evoke this consideration using a graphic of your own design. A down-arrow pointing to the centre of a cog/gear, perhaps. This may provide enough suggestion that the download will affect the (what's commonly interpreted as) settings & preferences.
Alternatively, and more convoluted still, could be to include perhaps layers of a globe in the background, a phone in the foreground, and a 3D arrow directing from the back to the front... though the point of iconography is to display quickly, easily recognisable shapes and objects to perform visual cues to someone new to your system.. so this may not be ideal.