If your dishwasher is installed under a countertop, it is most likely fastened with screws from below. To remove the dishwasher, you will first need to disconnect the power and water supply lines. Then, using a screwdriver or drill, remove the screws that are holding the dishwasher in place. Finally, lift the dishwasher out of its installation space and set it on a flat surface.
If your dishwasher is not installed under a countertop, then it is probably sitting on leveling legs. In this case, you will still need to disconnect the power and water supply lines before attempting to move the dishwasher. Once the lines are disconnected, simply tilt the dishwasher back on its legs and roll it out of its current location.