The thing to remember is that the as part of the upgrade process you will need to break and re-create the server farm.
This article, http://technet.microsoft.com/en-us/library/jj966220.aspx, has the steps involved for both a single server farm and for multiple server farm.
But basically its:
- Down load the patch
- Remove the Server from the farm Remove-OfficeWebAppsMachine
- Install the patch
- Re-create the server farm New-OfficeWebAppsFarm -InternalURL "http://...." .....