Single space lines in a document
Quickly single space your entire document using the Paragraph Spacing button on the Design tab.
Click Design > Paragraph Spacing.
Choose No Paragraph Space.
This overrides the settings of the style set you’re currently using. If you decide later that you’d like to return to the original settings, click Design > Paragraph Spacing again and choose the option under Style Set. The option may be Default, as shown above, or it will show the name of style set you’re currently using.
Single space part of a document
To single space only part of a document:
Select the paragraphs you want to change.
On the Home tab, click the Line and Paragraph Spacing button.