In Word 2007:
1. Open Microsoft Word
2. Select the Windows button on the top left
3. Select the Word Options button on the lower right of the menu
4. Select Save from the list on the left menu
5. Choose Word Document (.docx) or Word 97-2003 Document (.doc)
6. Click OK

In Word 2010:
1. Open Microsoft Word
2. Select the File tab on the top left
3. Select Options on the lower left section of the menu
4. Select Save from the list on the left menu
5. Select the drop-down menu for Save files in this format
6. Choose Word Document (.docx) or Word 97-2003 Document (.doc)
7. Click OK