Log into Office 365 (If not already logged in)
In the upper right hand corner click on the OneDrive tab, this will bring up the list of all of your documents
Click on the document you would like to edit
You will then see your document in only a read-only format
Click on the upper left hand side on Edit Document, this will bring up a drop down menu
Click on Edit in Word Online
This will then open the document in Office 365 online
The document is now able to be edited