Please dont send me the link to "how to change your header image" because I have been starring at it for over an hour with no idea on how to do it

I have an image that I want to use as my header. On my computer i saved it in its own file called your_header_image. That folder is connected to the whole shabang of 'includes' folders I just load that picture folder to my server or what do I do. IF I load anythign to my server once it gets there do I delete the original file on the server and replace it with this new one?