Not hard, Ilene, you just need to know where to look.
When you do a reply, above the box you are typing into, there is a font selection, size selection and color. In order to do size or font, you need to enter your text between the beginning and ending brackets or into the box that shows up.
What I usually do is type what I want to say, then highlight it, click on size and then select my size. Then when I have that, I highlight it all again, and select my color. Then, I highlight again and select center to have it centered on the page.
Now that I've said all that, I'm curious to see if someone has an easier way to do it.