How do I remove mold from window tracks?

Use vinegar! Vinegar will break down or dissolve about anything, and it’s easy to wipe up the gunk with folded paper towels.

Yep, vinegar and a toothbrush. Wipe off with paper towels. Vinegar kills mold spores.

If the dirt is being stubborn try some baking soda with the vinegar.

Bleach is a cleaner, does not kill mold. I don't use bleach at all. For washing whites I use hydrogen peroxide along with detergent.

Take an old toothbrush and heat up the neck with a lighter or a low heat gas stove and bend the neck 90 degrees so that the bristles are pointing down. Somewhat like a letter L.

Mechanically removing the mold is as important as killing it.

Vinegar kills the mold spores, bleach will not. Use and old toothbrush to scrub and loosen the debris. You could also spray it on to start the cleaning process. I would also consider wearing a mask to keep any free spores out of your lungs.