What you gain by converting to PNG
A JPG that has been converted to PNG does not get sharper. The detail JPEG compression threw away stays gone. What you get is a format that stops any further quality loss: PNG can be opened, edited and saved again as many times as you like without degrading.
That is the main reason to convert. If you plan to edit a picture in several rounds, add text on top, or place it in a design file, start from PNG so each save keeps the pixels exactly as they are.
Expect a bigger file
PNG stores pixels without discarding data, so a photograph saved as PNG is often three to ten times larger than the JPG it came from. A 500 KB JPG could turn into 3 MB. That is normal and not a sign that something went wrong.
If size matters more than editing flexibility, stay with JPG or try WebP, which handles photos far better. Use PNG when you need exact pixels, such as app screenshots, diagrams, pixel art, or sources for a logo.
Transparency does not appear on its own
PNG supports transparency, but converting a JPG will not create any. The result has the same solid background as the original. To get a cutout with a see-through background, run the picture through the background remover, which outputs a transparent PNG.
Where PNG is required
Some design tools, game engines and website builders prefer or require PNG for icons and overlays. Print shops sometimes ask for PNG when text and line art must stay sharp. Check the accepted formats of the destination before choosing.
Metadata such as camera details and GPS is not kept after conversion, so the PNG is also a cleaner file to share publicly.
Practical reasons people convert
Designers often convert a JPG to PNG before layering text over it in an editor, so repeated exports do not slowly eat the picture. Teachers do it for screenshots that will be marked up and re-saved several times.
Others need PNG because a website builder, a presentation tool or a sticker printing service lists it as the accepted type. In those cases the file looks identical, and only the container changes.
If you convert and the file gets too heavy to email, resize it by percentage. Halving the width and height cuts the pixel count to a quarter.
The converted file keeps your original name with a new extension. When you convert a batch, check that two files did not end up with the same name in the ZIP, for instance IMG_001.jpg and IMG_001.JPG, since some systems treat these as one.