Select and double-click on the text box so you are in text editing mode. Highlight the letters on which you wish to increase/decrease spacing.
Adjust the spacing between letters by holding down the arrows by kerning in the letter spacing area until you’ve reached your desired spacing. Or, enter in the exact spacing value if you’d prefer.
Also note that you can adjust this for individual words in the text box by highlighting just certain parts or by selecting the whole text box at once.