When it comes to image resolution, DPI by itself has very little meaning. This is usually a meta tag embedded in an image file that stands for dots-per-inch and is only relevant when you know the print or display size of the image. That means even a high-resolution photo can be rejected for publication, for example, if they are only looking at the DPI value in the file details. It’s very easy to change DPI in apps like GIMP, Paint.NET and Photoshop. However, if you really don’t want to install another app, you can change the DPI in Microsoft Paint, provided you have another image that has the DPI you need. Keep in mind that changing the DPI by itself does not enhance or reduce image quality.
Using MS Paint