If you are planning on replacing your laminate countertops--that is, putting new laminate over the existing laminate or substructure--the first step is to make sure the existing surface is both smooth enough and sound enough to make the project worth your effort. Remember, installing new laminate is a painstaking process, but if it's done right, the end result can light up your kitchen for years to come.
To begin, you need to clear your countertops of everything, including the kitchen sink. Close the shutoff valves under the sink and then disconnect the faucet from the water lines and the sink from the drain line. The sink is attached to the countertop with clips, which you can unscrew to lift the sink out.
Cracks, deep scratches, and gouges in your existing laminate will, over time, show through the new laminate, so you need to either remove the old laminate, or cover it with 1/4 inch plywood. Installing the plywood is tedious. Removing the old laminate is really really tedious, but keeps the counter on the same plane, which is important if you are working with an existing backsplash.
If you opt for plywood over the existing laminate, cut it slightly (about 1/4 inch) larger than the counter you are covering, then sand it flush after installation. Use construction adhesive to attach the plywood, then add screws every six inches into the cabinet frame. Countersink these screws and use wood putty to make the plywood perfectly smooth.
To remove old laminate, use a heat gun and a putty knife. Using a putty knife that is at least 4 inches wide makes it easier to get the old laminate up in fewer pieces. Keep a fire extinguisher handy just in case the heat gun ignites the old laminate. When you have removed all of the old laminate, thoroughly sand the plywood underneath until it is perfectly smooth.
If you have never used contact cement before, you might want to do a test run with a scrap piece of wood and laminate just to get a feel for it.
Note: Cut the sink hole after attaching the laminate to the countertop. Drill a hole in the center, use your trim router to cut the sink hole, and then replace the sink.