Lift up slightly and slide it away from the SATA port. Use a small prying tool, or anything thin and flat (preferably plastic) to lift the drive if you can't grip it.
The M2 is above it in the photo, the small empty slot and the 1 screw to hold it down.
Normally there is a piece of plastic that pulls the HDD up a bit, and then slides out. But as said above, just lift it slightly and it will slide.