To change spaces between words and letters, please check changing spacing between letters or words. However, please follow the steps below if you need to change the spaces between words only, but not the spaces between letters.
Step 1: Select the document using "Ctrl+A" or click "Select All" from the "Home" tab;
Step 2: Use the shortcut "Ctrl+H" or click the "Replace" command in the "Home" tab (see above) to open the "Find and Replace" window;
Step 3: Type one space in the "Find what" box, and type 2 or more spaces in the "Replace with" box;
Step 4: Click the "Replace All" button to change the spaces between words.