Here's a caveat on that: If you are trying to resize your text inside the Story Editor, it's a pain in the bezinkus. In the Story Editor (which is a somewhat clunky beast) you have to select your block of text and then move the font size indicator only ONE SIZE, which will work. Then, to move it another size, you have to select it again. This is all because the Story Editor is a piece of work nobody wants to finish. Unless you have a later version which is improved, but I understood the Team to say they aren't working on the Story Editor.
It is much easier to change the font size using the properties window. If you want to change all of the text in the frame, you can just doubleclick inside the frame, and change the size to whatever you want, and it works! Unlike Story Editor.
If you want to just change part, you select the part before you open the Properties Window.
Pressing F2 opens the Properties Window. Then, you have to drill down into the text menu, and change the size, but there is no problem with this as in the Story Editor. Press F2 again and the properties window will go away.