DPI (pixels per inch) controls how large the same pixels print. Changing the metadata number does not add detail.
How to check your image
Note width and height in pixels, choose a target DPI, and compute inches = pixels ÷ DPI. If the print is larger than that at your quality target, expect softness.
Upscaling limits
Software can invent pixels, but it cannot recover lost optical detail. Smaller prints or greater viewing distance are the reliable fixes.
FAQ
Can I just change 72 DPI to 300 DPI?
Changing the metadata number does not add detail. You need more pixels or a smaller print to increase effective resolution.