In latest Word versions: Word 2007 and Word 2010, you will find the superscript and subscript options right on the ribbon. So, if you’re creating a document that contain lots of chemical formulas and other characters which are to be subscripted or superscripted, you will need to click respective button under Home tab.
To change text into superscript, select the text, character or letter which you want to change and from Home tab, in Font group, click Superscript button.
It will change the text into superscript. For changing into subscript repeat the procedure, select the text and in Font group, click Subscript button.