Are you grounded? If yes, take one of the new memory modules and align it with the connector by the correct side: the close-to-the-middle indentation of the module has to face the highlighted pin.

Then, keeping it tilted and carrying on the "pendulum" movement, gently push the module inside the slot. STOP when you feel you can't go any further: the new memory module should be now tilted and totally inside the connector - as it is shown in pic#2 - and the indentation of the module should almost be attached to the centring pin.

Once that the module is so positioned, gently press it down pushing it in the middle with your fingers until you hear a loud click: that sound means that the retaining arms have correctly grabbed the module and that the latter one has been successfully inserted!