By weight, Ice takes up more space than the same amount of water. Displacement is why it floats in addition to air bubbles and the like. If the ice on the water melts, the ocean levels would drop.
If all the ice in the world melts we are all dead because that means the earth in the temperate zones is probably 200 degrees, to get BOTH poles above freezing, so let’s not worry ourselves about that happening.
The Greenland Ice Sheet is about sea level.