In order to gain access to the appliance feet, you will need to tilt the washing machine back and prop it up. A block of wood serves this purpose well. Lean the washing machine back and use a small 2-by-4 block of wood to support the unit up off its front feet first. After you have replaced the feet or pads on the front, pull the unit out and do the same for the back.
Most appliance feet work in about the same fashion. They have a long threaded shaft that turns and raises or lowers the foot in order to raise or lower the appliance. Turning the foot counterclockwise should extend the foot and eventually remove it entirely. Take the foot to a home improvement store and match it with universal replacements. If you cannot find a properly sized part, you will need to order it from the manufacturer.
If the foot is otherwise functional and undamaged, you may want to consider replacing the pad itself. It can be difficult to find properly sized pieces of padding for appliance feet. Check your local hardware and home improvement stores and, failing that, consider cutting a small piece of felt and adhering it to the foot yourself using strong adhesive.
Before replacing the washing machine foot or pad yourself, check the user manual for the manufacturer's website. Make sure the unit has not had any recalls for its feet or pads. The manual may also list a website or location where you can order replacement parts. Additionally, the manufacturer's website should be able to point you in the direction of an authorized service center that may be able to order any parts you need.