If you want to change line spacing for the entire document, press "Ctrl-A" to quickly select all text. On the Home tab, click the "Line and Paragraph Spacing" button found in the Paragraph group.

You can also set the spacing between paragraphs in a single document or in the template. By default, Word 2011 inserts 1 1/2 spaces between paragraphs.

Whether you prefer one space or two at the end of sentences, Word can help you apply that preference consistently.