Column and Row Header text

Can someone tell me how to edit the text displayed in the column headers (A - ZZ) and the text displayed in the Row headers (1-6553?)

Basically, I have done this in the past, and i do not remember how to do it. I am trying to figure out how to get the text in these sections to be smaller. I'm not sure how to explain what I am trying to achieve.

Let me know if i need to explain further.

Thanks.

You'd think they would make this stuff a little more obvious.