There's plenty of tools out there that helps with Image optimization.
For a DIY job, I'd recommend Photoshop. This is not free software though.
A free DIY route would be https://www4.lunapic.com/editor/ although it looks a little outdated, it offers all the features needed to optimize your images.
A paid route would be Cloudinary, you may find their tool here really useful. https://webspeedtest.cloudinary.com/ it's only really there to tempt you into using their paid service, but the tips you get from this analysis alone will help you greatly.
The paid version will basically resize the image based on the user's device, convert to the lightest format, etc. It takes much of the headache away but it's quite expensive. Cloudflare also offers a similar service too.