How do I increase the DPI of an existing image?

You cannot truly add detail to an image that is not there. Changing the resolution number in an editor only stretches the existing pixels, so the image gets bigger without getting sharper.

• Bumping a file from 72 to 300 DPI in Photoshop just spreads the same pixels over more inches.
• The best fix is to go back to the original high-resolution source file or re-shoot the subject.
• AI upscaling tools can help in a pinch, but results vary and fine detail is often invented rather than recovered.
• Plan for print resolution from the start so you are not enlarging a small file later.