Open your Word document
Press Ctrl+A to select all text
Go to the Home tab
Click the Line and Paragraph Spacing button
Select 2.0
Or press Ctrl+2
To double-space only part of the document, select the text first
Go to the Home tab
Click the Line and Paragraph Spacing button
Select 2.0
Or right-click the selected text
Choose Paragraph
Set Line spacing to Double
Click OK