Try checking out image optimization on your website. Some stats say that is one of the most common causes of slowing websites.
Consider the following things:
1. PNG image files are often needlessly large. PNG images can be optimized using free tools like pngcrush that reduce the size of the file without changing or reducing the image quality.
2. The same with JPEG files, but use in this case another tool – jpegtran.
3. PNG files are better be used for icons and logos while JPEG is preferable for photos. Because PNG images support transparency while JPEGs do not, the PNG format is commonly overused for images that are better served as JPEGs. By utilizing JPEG instead, you will do a good saving in terms of file sizes on your website.
