Please tell me how to do this because it is important to me...?!?!.?!?.
If by 'icon' you mean avatar, then you simply need to go to 'Edit Profile & Settings' and click on 'Change picture', and then on the orange 'Upload a new picture' button.
Keep in mind that the standard limitations for uploading images to Stack apply - maximum size is 2 MB, and the image should be suitable for work. It should also be square, otherwise the aspect ratio might get mangled and distort the picture.
