Header

I have repeatly tried to change the header on my site, blackgirlguide.com, using 300 x 90 and 90 x 300 measurements and I can’t seem to change it! Is there any way that I can alter the original logo that says “Corporate” to read “Black Girls Guide” since my attempts to upload newly created ones in Photoshop did not work? I really like the one that came with the theme.

In addition, I am trying to get rid of the text under the comments box that reads:
You may use these HTML tags and attributes: <abbr title=””> <acronym title=””> <b>

Thank you!