I haven’t tried it, but Gimp is free software for photo manipulation that seems to have a good reputation. I use Lightroom Classic, but that is not free. If you lift the shadows, you will probably get additional noise, so may need to add some noise reduction. You also be aware that JPEG is a lossy format and repeated saving of files depletes quality. It is worth keeping an original that you can go back totter experimenting with processing and finding what works best for you pictures.