How can I upload my DEM to Google Earth?
Agisoft Photoscan allows exporting Google Map tiles in Export DEM option but I have no idea how to upload it to Google Earth.
Google earth needs KML and KMZ formats for direct uploads.
You can make your DEM an image overlay and manually place it on the area of interest on the map. I linked a resource below that might be helpful to you.
If you want to add your DEM as a replacement for Google Earth's built-in 3D terrain, unfortunately that's not possible.
That said, there are some options for visualizing DEM data in Google Earth. You can turn your DEM into a raster visualization with techniques like colored shading for the different elevations, or contour lines of some sort. Once you do that, and produce an RGB color image, you can bring that into Google Earth or Maps in a variety of ways (as mentined in the other answer). If you turn your DEM into vector data like contour lines, you could bring those in as well (as KML, or import as shapefile into Earth Pro). Another option, if you actually want to see your 3D terrain data in Earth is to turn it into a KML compatible 3D model (colada file), and bring that into Earth Pro. To see it correctly, you'll either need to turn off Earth's built-in terrain data, or raise your terrain up enough so that it does not intersect the built-in terrain.