My site is www.thehealthyhostess.com and I would like to change my post title and widgets to uppercase arial?
Can you help?

did you look thru the theme options?

Yes, I was able to change the menu font but couldn't find where to change the other font options. Did I miss something?

ATO->Style POST & PAGES->HEADLINE Box: XXXXX
ATO->Style WIDGETS->Widget Titles

So I just type in the font style I want and uppercase with the size?

If your not sure about CSS, I suggest you take a tutorial. A good one can be found at htmlhound.com
If your not wanting to try things, then you should hire someone to do it for you or train you.