To quickly answer your question, right-click anywhere on the page then select "Paragraph" from the menu. From the resulting menu, go to the "spacing" section (near the center) and click on "Line Spacing"...then select the spacing you desire.

FWIW, if you are going to work with Word in your retirement years, you may want to review Understanding styles | ShaunaKelly.com. Understanding that information will help you tremendously in formatting your documents.

HTHs...