DPI is a field stored in the PNG file BUT that field is frequently ignored and overridden. 72 DPI is standard monitor display resolution. If you have a 1024x1024 image it is 14+ inches wide on your monitor but when printed on a 300DPI printer is 3.41 inches. Similarly, 4096x4096 is 55+ inches wide at 72DPI and 13+ at 300DPI. It just depends on how you want to interpret and present that block of dots. If you really want the PNG file to report 300 DPI the free and easy way is to use gimp. Bring the file in then select Image->Scale Image, leave the width and height alone, select pixels/in in the resolution dropdown and set 300 in the X/Y resolution fields. Then export the file and it will be saved with those field settings. When you import the image into Printify, use either the Width and Height or Scale fields to control the size of your design image. Hope this helps. 🤠