When PNG makes sense
PNG does not lose quality each time you save it, so it suits editing, screenshots and logos. It does not make a blurry JPG sharper.
Convert with PicFitter
Use the JPG to PNG converter. Select your files and download the PNG versions.
Expect larger files
A PNG made from a photo is often three to five times larger than the JPG. If size matters, convert to WebP instead.
Convert without a tool
Open the JPG in Paint (Windows) or Preview (Mac) and save or export as PNG.
Common problems
Expecting transparency (a JPG has none, so the background stays), and expecting better quality (conversion cannot restore lost detail).