Do I need to sand the paint on my cabinets before repainting?

I would take one of the cabinet doors off and take it to the paint department of your home improvement store and ask them what products to buy and how to apply it.

Only if you want the new paint to stick.

You definitely want to get the sheen off of the cabinets before you paint them, that may require sanding, or stripping, and they make a product called Liquid Sander that you just put on and paint over.

It's always good to give a light sanding to give it tooth use (150 or 220 grit) and be sure to clean all dust off before painting

It's definitely a smart idea to lightly sand before priming and painting to make sure the job sticks