Optimize PNG images
You can also use: http://ezgif.com/optipng?url=http://link/to/image.gif
Online PNG optimizer/compressor
The PNG optimizer can losslessly compress and reduce PNG image size. It can be used both for standard, single-image PNG images, and for animated PNG (APNG).
It's very advisable to optimize images used in web, as it can save bandwidth and make websites load a little faster.
The actual size reduction percentage may vary depending on what optimizations have been done previously for a particular image, but it can reach more than 40% in some cases, so give it a try.