Need to reduce file size in my media library

I have literally thousands of image files in my website's media library, and they're all high resolution jpegs, averaging a full megabyte each. I've finally come around to the realization that my blog doesn't need quite that much picture quality, especially not on mobile devices, so it's slowing down my page load times for no good reason. Clearly, it's time for me to take a different approach. Does anyone know of a plug-in or process that will let me selectively edit my existing media library to reduce the size and/or resolution of the images therein? (Hopefully in bulk, as opposed to file by file).