Pull the clip/pin out. In your second pic, you can see the top of it. I'm not sure what its called, but its like a reverse cotter pin, it goes around the outside edges of the freeze plug. Once the pin is out, pull the plug out. Beware, coolant will be coming out so either bleed some off or have a bucket ready.
once the old one is out, put the new gasket on and put the plug back in. It may take some "motivating". once its in, pop the pin back in.
'14 Tuxedo Black ST3
'13 Ingot Silver Escape Titanium AWD
'04 CD Silver SVT, #877, 1 of 135 May 2011 ROTM, FF11: Best Display, Best of Show; AFN12: Best SVT, Best Audio, Finest Five, Carlisle Nifty Fifty