HTML in main page template

I had completely forgotten what HTML to use -- and where to put it -- to enlarge my blog title text. In addition, if I wanted to substitute an image in place of the regular blog title text, where would the image HTML be placed in the main page template?

Thanks much in advance.

UPDATE (1519 EST): Figured it out (changing fonts and sizes for my title banners, that is) after much playing. Think knowing where to place this code will eventually clue me in on where to place proper image code when time comes. :-)