Text sizes can be adjusted in three ways: the point size of text (which increases both the height and width at once), just the letter height, or just the letter width. To adjust these, you will need to have the whole text box selected and not be editing the text box.
To adjust both the letter height and width at the same time, adjust the point size of the text in the Text palette.
To adjust only the letter height (not the width), adjust the values in the Letter Height box in the Text palette.
To adjust only the letter width (not the height), adjust the values in the Letter Width box in the Text palette.