The PNG graphic format started way back in January of 1995 and slowly grew as a better alternative to GIF and TIFF formats. Even with large image resolutions, PNG allows smaller file sizes through a loss-less compression algorithm. In recognition of this advancing format, Microsoft included PNG support in its native Paint program, which can be used to change PNG resolutions. However, like any raster, or pixel-based, format, increasing resolution is possible only with a degradation of image quality, but decreasing resolution experiences no such loss.
Click the "Start" button, "All Programs," "Accessories" and then "Paint."
Hold the "Ctrl" key and press "Open" to invoke Paint's "Open" dialog window. Navigate to the folder containing your PNG file and double-click it. If you need to filter down the list of images, click the "All Pictures Files" button and select "PNG (*.png)" to display only PNG files.
Click "Resize" in the "Image" group of the "Home" tab.
Click either "Percentage" or "Pixels" in the "Resize and Skew" windows to select the type of scaling. "Percentage" allows you to resize your image as a percentage of the original size. "Pixels" allows you to select an exact size.
Check "Maintain Aspect Ratio" to prevent distorting the image by changing one axis more than the other.
Enter the desired size as a percentage or the actual resolution, depending on your previous selection. You only need to enter the "Horizontal" or "Vertical" dimension, and the other will be automatically filled, as long as "Maintain Aspect Ratio" is checked.
Click "OK" to resize the image and close the "Resize and Skew" window.
Hold the "Ctrl" key and press "S" to overwrite the original file with the newly changed resolution. If you prefer to keep the original, click the top left document button, select "Save As" and enter a new file name. The PNG format will automatically be selected.