Many people find DPI confusing, believing that a larger DPI will increase image quality or event the file size. In fact DPI does not affect the on screen image quality or file size.
DPI is simply metadata of the image that specifies how many pixels of the image to print in each square inch of paper. Therefore to match the international standard for printing high quality photos we have set the DPI of our screenshots to be 300.
Alternatively if you want to improve the quality of a image you can change the format and quality parameters. Or if you want a more detailed image you can increase the screenshot resolution.