PNG is lossless - so how does it get smaller?
PNG never throws away pixels, so the biggest wins come from reducing dimensions or switching to a more efficient format. Aimager lets you resize a PNG and re-encode it, and for photographic PNGs converting to WebP or JPG can cut the size by 60-90%.
Keep transparency intact
If your PNG has a transparent background, keep the output as PNG or WebP to preserve the alpha channel. Converting to JPG removes transparency, so Aimager asks you to choose a background colour first.