Installation 
  2.5 Installing on the S7-1500 standard rail 
SCALANCE M874, M876 
Operating Instructions, 06/2015, C79000-G8976-C331-05 
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1.  Disconnect all connected cables. 
2.  Using a screwdriver, pull down the catch on the rear of the device. 
3.  Remove the device from the standard rail.