Dell Precision M40 - Manual (Page 58)

2. Close the display, and turn the computer upside down.
3. Remove the screw from the memory module cover (located next to the icon labeled "K/M"), and remove the memory module cover.
4. If you are replacing a memory module, remove the existing module.
Carefully spread apart the inner metal tabs of the memory module socket, and then lift the memory module away from the socket.
5. Ground yourself and unpack the new memory module from the upgrade kit.
6. If you need to install memory modules in two sockets, install a memory module in the socket labeled "JDIM 1" ("DIMM A") before you install a
module in the socket labeled "JDIM 2" ("DIMM B").
If you have only one memory module, install it in the "JDIM 1" ("DIMM A") socket.