Laminate flooring is a veneer of hardwood, laminated over a composite material like particleboard. If the laminate surface of the flooring wears out, you can't use a drum sander on it as you can for a solid hardwood floor, because you risk sanding through the veneer. You can add a new polyurethane gloss layer by lightly sanding the surface to remove any remaining shine, then applying the new gloss over it. The floor must be clean and dry before you start.
Dull the surface of the floor with your vibrating pad sander. Run the sander with the direction of the floorboards, just enough to dull the shine.
Vacuum up the dust. Wipe up the floor with tackcloths to take up any residual dust.
Open your polyurethane and stir it slowly with a paint stick. Don't shake the can, as that can cause bubbles to form.
Pour a puddle of polyurethane in one corner, making it as wide as your floor gloss applicator. Pour it in a direction perpendicular to the boards.
Set the applicator in the puddle. Pull it slowly backward with the direction of the boards. Pour more polyurethane and continue spreading it, doing the whole floor. Let the polyurethane set for eight hours.
Buff the polyurethane by hand with fine sandpaper, very lightly, dulling the shine so the next coat will stick. Use tackcloths to wipe up the dust.
Repeat steps 4, 5 and 6 to lay and buff a second coat. Add a third coat, but don't sand it. Let it set for two days.