You can go over existing laminate with proper prep. Sand the existing laminate with and obital sander using 60-80 grit paper. You do not have to sand through the finish, but you want to scuff it up. Wash the laminate with a solvent to remove any wax, dirt or grease. I use lacquer thinner or acetone. Be sure to ventilate, vapors are strong and flammable. Both steps must be done to all laminate surfaces, including the edges. Check the surface for any foreign material. Everything will telegraph through the new laminate. Make sure it is clean. I use Hybond CF23 spray adhesive, but I think you will be using a roll/brush grade contact. After you fit the laminate, cover both surfaces with contact. Make sure coverage is 100%. Rolling gives better coverage. Don't cheat on the adhesive. Give it ample time to dry. Use slip sheets or spacers and put your pieces together. Drying time is extremely important when going over existing laminate. If it is put together too soon, the adhesive will lift from the top and it will not bond in that area.