You should always modify references in your Zotero Library, not in Word. Any changes made in Word will not be saved.
To modify a reference you can simply click in the fields of a reference to begin editing them. Changes will be automatically saved.
To add additional authors, use the plus button 
after the authors name fields or remove names using the minus button 
.
You can change authors to contributors, editors, translator etc. by clicking on the word ‘Author’ and a drop-down menu will appear:
You can reorder the author names using the waffle button to the left of the name 
If you want to create a collection, right-click on a title and choose ‘add to collection’ and ‘new collection’. Creating collections groups together various records which can be useful if you want to group together records for a particular assignment. After a collection is created it will appear as an option for future references.
Your collection will then appear as a folder in the left-hand menu and will be an option next time you want to add a reference to a collection.
