(With the computer off, of course) Un-clip the fan and set it out of the way. (You can probably leave it connected to the motherboard header.)
Then, install your ram in the slot closest to the heat sink.
Now, re-clip the fan to the heatsink higher up on the heatsink so that it clears your RAM.
Install the rest of your RAM, turn the computer on, and enjoy. (maybe run memtest just to check your new sticks)