Melting land ice, like mountain glaciers and the Greenland and Antarctic ice sheets, will change Earth’s rotation only if the meltwater flows into the ocean. For example, if the Greenland ice sheet were to completely melt and the meltwater were to completely flow into the ocean, then global sea level would rise by about seven meters (23 feet) and Earth would rotate more slowly, with the length of the day becoming longer than it is today, by about 2 milliseconds.
Melting sea ice, such as the Arctic ice cap, does not change sea level because the ice displaces its volume and, hence, does not change Earth’s rotation.