There's no automatic thing you can do to make the text and logos just "poof" disappear. If you want, you can try using the clone tool (looks like a stamp) by holding down alt and clicking on an area, then brushing over the section where the logo is—this should "clone" the area you clicked and pressed alt on, onto the area you brush it. It won't be perfect but that's the best I can think of, aside from just cutting off the section of wallpaper entirely.

Did my instructions make sense?