Remove the shelves from their supports if they are removable. Disassembly allows you to move your work to an open or well-ventilated space to do your work.
Clean the shelves with a general purpose cleaner. Rinse with a clean, damp cloth.
Sand the shelves with 120-grit sandpaper to degloss the surface. Deglossing ensures the new paint will stick to the old surface. Remove dust with a damp cloth.
Coat the shelves with semi-gloss or high-gloss enamel spray paint. Hold the can 8 to 12 inches from the surface at an angle. Keep the can moving while spraying to avoid drips. Spray thin layers of paint in multiple applications until you achieve the coverage you want.
Allow the shelves to dry overnight; then assemble for use.