Unplug the Mac mini and place it on a static free work surface.
Turn the Mac mini upside and using your thumbs to turn the circular black panel counter-clockwise until it reaches the open position.
Remove the black base then gently push on the two arms holding the RAM in place to release the memory sticks.
To insert the new RAM make sure the notch at the bottom of the memory stick matches the position of the notch in the memory slot. Push the memory stick into the slot at an angle then push down to make the arms click into place.
Once you have installed the new memory you can place the removeable black panel back onto the device in the open position. Using your thumbs rotate the panel clockwise until it moves to the closed position.
Plug your Mac Mini back in, turn it on, and you'll be up and running with your new RAM.