With both sticks out you are ready to put the new ones in. Each stick has a small notch on the left side splitting the gold contacts. This is for the alignment pin.

Starting with the bottom stick of RAM, align the pin and insert the stick at the same angle you removed the old one. Once it is gently pushed in all the way, push the stick down as shown in the third picture until it locks under the retaining springs.

Repeat this process for the second stick of RAM.