Changing the DPI number alone doesn't make a photo sharper. PixelEdit Pro adds real pixels with AI, up to 4x, and saves the file at 300 or 600 DPI so it prints sharp at the size you need.
Upload the image, pick 4x and download at 300 DPI. The AI enlarges the image so the extra pixels are real detail, not stretched blur.
Only if the image already has enough pixels. If it is small, raising DPI makes the print smaller; you need upscaling to keep the size and the sharpness.
Divide the pixels by 300: 2480 × 3508 px prints an A4 page, and 3508 × 4961 px prints A3.