If you use
- Caption Text
- Ribbon Text
and you type your text...
The full line will have the same size.
You can resize it with the mouse... as you would resize any object (it's a TEXT OBJECT).
If you use Journal Text you can set the size of the font...
Or do you mean when you use an alpha?... in this case select the letter, press the key S on your keyboard and set the width and the height (enter value)... do the same with each letter and always set the same height if the alpha is in uppercase.