Most writers single space. That way you see more text at a time. However, you might want to change line spacing for printing, because your recipient prefers double spacing, or for some other reason.
Luckily for everyone, Word makes on-the-fly spacing easy with quick keyboard shortcuts.
Highlight the text in Word. Use the following keyboard shortcuts.
Single spacing: [CTRL]
Double spacing: [CTRL]
For one-and-a-half line (1.5) spacing: [CTRL]