On the underside of your notebook you will find two service doors. If you remove the big one you will see this:
In the picture you can see one RAM module on the right side of the fan. Above the installed RAM module you see a second slot for another module. If you open your service door, you might find both slots occupied. On each side of the module is a metal hinge that fixes it. If you release both hinges simultaneously, the module will lift up slightly and you can take it out.
To insert a new one, place it into the empty slot at the same angle like the removed module had after you released the hinges (take care for the notch in the module). Press it down and the hinges will catch it.
During the whole process take care not to touch the pins of the RAM modules or any other electric conductor. It would also be best to ground yourself before starting this work.