How to a remove/replace an image?

[Timbow]

You upload the new image if it isn't already on the web, then you find the markup or the css which defines the old image url and you alter it to the location of the new one. 

Maybe you can do it through the page editor, maybe it's in a component, maybe a template file and maybe a css file. It might even look like an image but actually be stored as a font glyph.