The Easiest Way to Update Your Documents

(1) Go to Media (by clicking Media on the menu) and then (2) search for the name of the doc you're replacing (in the example, I just put in "dress" )  and then (3) click the document that you want to replace (in the example it's the dress code).  (scroll down)

Then you just replace the document with your updated copy:

Browse for your file, and then just click "upload" and you're done.  You can leave the two other settings alone.