I have a cool icon for my minecraft server but i dont know where i can upload it o so i can change my icon if anyone knows how to please explain.

You should upload it as server-icon.png to main server folder(Where server.properties file lives)

Did it and it does not work for some reason. I did everything right and checked the format but it still does not work.

Please try 64x64 pixels size.

It workss! Thank you so much...