I love Paint.net for resizing and simple photo editing, but it's not very effective in lossless image compression. I recommend using online tools like:
https://compressor.io/compress
http://optimizilla.com/
https://tinypng.com/
(I wrote a guide about this for a client once, so I remember these by heart)
but you don't need lossless for JPG's you upload to sites like these + it takes time to upload them to the online compressor. (It's another matter if you intend to sell prints ofc... but then you are going to use the original file anyway).
But thanks for the links :) It's definitely useful for users who don't have any image processing software at hand.