Remove the bottom front kick plate (the metal cover across the bottom of the front under the door) and you will find a water connection which needs to be removed (turn the water off first) and an electrical connection (if there is a cord and plug, unplug it; if it is hardwired, make sure that all power to the dishwasher is ‘off’ before removing the electric supply).
If you do not understand what I described, do not do this yourself. Either call a plumbing contractor, electrical contractor, or just have the new dishwasher installed by the appliance installers from the store where you purchase your new dishwasher.