Nobody likes images that take a lot of time to load. For webmasters it means more bandwidth usage and hence more cost. Therefore it is always a good idea to keep the size of your image as low as possible without affecting the image quality. You can do that if you have good Photoshop skills, but if you are not a photoshop expert or would like to save some time, I would recommend using PunyPNG.
PunyPNG is an online tool that reduces the size of an image by converting it to a highly-compressed PNG. Simply upload your GIF, JPEG or PNG image and let PunyPNG compress it for you without losing any quality or details. You will also be able to see the original size of the image, the final size of the image and the percent reduction in size.
After the image has been compressed, you can simply download it. You can upload any image with max file size of 500 KB. You can also use this tool as a simple JPEG to PNG converter.