Increase or Decrease Text Size in Word

To increase the text size, select the text and press Control + Shift + Full Stop (.).
To decrease the text size, select the text and press Control + Shift + Comma (,).
Keep pressing the shortcut to go up/down in increments, until you reach the required size.
If you are struggling to read a document, because the text is too small, press Control + A to select all and Control + Shift + Full Stop until you can read it comfortably.