There are two wires connected to the water inlet valve (four, if it has two solenoids). Label the wires and connections so that you can properly reconnect them later. The wires are connected with slip on connectors. Firmly pull the connectors off of the terminals (do not pull on the wire itself). You may need to use a pair of needle-nose pliers to remove the connectors. Inspect the wire connectors for corrosion. If they are corroded they should be cleaned or replaced. If the valve has a grounding wire remove it now.
In some cases you will replace only the solenoids, otherwise the entire valve is replaced. In either case, it usually easier to make the repair with the valve removed from the dishwasher. The valve is fastened to dishwasher frame with two or more screws. Remove the screws and valve.
If you are only replacing the solenoid(s), remove them now from the valve assembly and install the replacement. Install the new inlet valve and reconnect the ground wire, hoses and remaining wires. Replace the access panel, turn on the water supply and restore the electricity.