There are a few ways to alter the size of your text. The first is to highlight the text and then use the text size drop-down box that becomes available, as shown here:
Another way is to highlight the text, then double-click on the text size, and then use your up and down arrows to alter the text size. It will choose the default text size options, such as 8, 19, 10, 12, 14, 18, 22, 24, 30, and so on.
Note that "up" makes text smaller and "down" makes text larger, that is, it simulates how you need to move on the size chooser rather than taking the text size up or down.
The third option is to manually type any size you want; just double-click ...