Sample image: Before and After. Scroll down to see how it was done.
This works whether you're making simple color balance adjustments, adding shadow detail, applying a bit of clarity or a combination of all of the above. And, it has robust black-and-white conversion tools.
While Lightroom can handle JPEGs, there is more information you can work with in a RAW original. When you've finished, you can convert the image to JPG, and open it in Photoshop to make further changes if needed. I generally shoot RAW + JPEG. It may require more storage, but hey, storage is cheap. Don't worry about it.
Adobe Lightroom CC is available as a download under a license agreement that costs a few dollars a month. I recommend the Lightroom/Photoshop package, which is collectively less expensive than buying a disc, and is updated at no additional cost as part of the deal.
Case study: A portrait session
I recently had a fun portrait session with Leanne, using a big Zeiss 85mm f/1.4 lens at its widest aperture so I could get the effect of using a super-narrow depth of field. The images straight out of camera were great (mostly because Leanne is former Miss Long Island beauty pageant queen, and she loves the camera), but I wanted to see how she'd look in glorious Black and White.
I imported all of my RAW files from the session to Lightroom and got to work. Let's take a step-by-step look at one way to reinterpret a color original as a classic black and white image.