Optimize images on my PC and then upload to server

Hi

I am on Windows 7 and i am looking for a way to optimize my users avatars (.jpg and .png) on my pc and then upload them back to the server.....

I don't want a huge compression level and about 20% down will be great as i want the images to look good.

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A few softwares that i try they force me to rename the new files and they are thousand and on another software the images are not looking good

What you can recommend me and what you use for your images?

If there is a better solution for Linux just let me know

Thank you

 

Does it offer lossless optimization?

I like to get a 15%-20% smaller size about, not huge compression but i don't want to get images with pixels