What is the best way to update a WDS wim file from windows 10 version 1607 to version 1809?

Hello

I have inherited a windows deployment from a previous employee.  I am learning as much as I can but do not have any one to ask questions and was hoping you could point me in the right direction. 

I have an MDT 2013 deployment share with a windows 10 version 1607 Wim file. Does anyone know what the best way is to update that file to the current version 1809? 

1. Is there a way to just add the update to the Wim file:
2. Run it as an application and add a task sequence?
3. Or does the image need to be redone which I am not sure where to start on that yet either.

I have several computers that have not been updating to the newest version and I want to try and avoid having to manually update in the future. Any guidance would be greatly appreciated.

Thank you

Todd