Wipe away any surface grease and dirt from the vents with a dry, clean cloth. The dirt and grease may smear a bit, but it will be removed later.
Fill the spray bottle with white vinegar. Vinegar is a natural grease-cutting agent and is safe for most surfaces.
Dampen a clean cloth with warm water. Spray vinegar onto the cloth until it is fully saturated. Wring out excess vinegar into the sink.
Wipe away surface grease and dirt from the vents. Using an edge of the cloth, clean in between the slats of the vents. Do this until the vents are clean.
Rinse away any vinegar residue from the microwave with a clean cloth dampened with warm water.