There are many free online services that will compress images for you.
I use and recommend https://tinypng.com
TinyPNG uses smart lossy compression techniques to reduce the file size of your PNG files. By selectively decreasing the number of colors in the image, fewer bytes are required to store the data. The effect is nearly invisible but it makes a very large difference in file size!
Use the optimized image to save bandwidth and loading time and your website visitors will thank you.