[@Mildgyth](/forums/dis/topics/ask-the-mods-anything?post_id=5209656#post_5209656)
Saving a JPEG as PNG isn't bringing the lost details back. The JPEG compression artifacts can actually make the PNG larger, since it can't deal well with the artifact color fringing. If all you have is a JPEG, keep it as a JPEG. Unless you can find the original *non-lossy* image, the lost details will be eternally lost.
In other words, don't bother reuploading the image. You'll only waste disk space and bandwidth.