How do I remove mold from wooden window frames?

First wash with soap and water and then wipe with vinegar, Kimberly.

Clean with a 50/50 vinegar/water solution. You may want to start using DampRid in the bathroom and change out regularly. It will work wonders to absorbing the water in the air to prevent the problem in the future.

You should be able to clean the mold off with you choice of bleach solution, vinegar solution, hydrogen peroxide solution etc. That wouldn't be enough reason to throw the window away. (However if the actual wood frame is spongy and you can push a screwdriver through the wood, then you might need to repair it. ) Once you have the window mold free with your cleaning, let it dry all the way through and then seal it with varnish or paint, to match the window.

Plain old white vinegar. Vinegar kills the mold spores.

https://www.servicemaster-restoration-cleaning.com/2017/03/mold-myths/

Since there is no exhaust fan, I would consider installing one. Crack the window, use a portable fan to ventilate the area after showering.

I totally agree with Naomie, you nee air circulation in the bathroom to take care of the moisture, even a portable fan should suffice. Beach water will help clean the area, and vinegar will kill the spores, let it dry on the window frame to kill as much as possible. When you clean the bathroom, go over the window frame with vinegar and you may prevent it from coming back.