Here are some steps to patch your Office Web Apps servers to the very recently released Service Pack 1 build. I have tested these at a few clients. Let me know if you have any problems or questions.
Firstly read this article and understand the steps involved: http://technet.microsoft.com/en-us/library/jj966220.aspx
Here are the steps to follow:
1) Remove the WOPI binding from the Central Administration server using the following PowerShell:
2) Remove the machines from the OWA farm, to be run for each farm in the OWA farm (effectively scrapping the farm) :
3) Patch each OWA server with OWA SP1 and reboot each OWA server.
4) Recreate the OWA farm on the First OWA server using the following PowerShell command. Make sure that you have the -SSLOffloaded parameter specified if you are using a load balancer. (Reference: http://technet.microsoft.com/en-us/library/jj219436.aspx)
Change to suit your environment of course:
5) On each subsequent OWA server run the following PowerShell to rejoin the machine to the farm:
6) On the first OWA server run the following PowerShell to do a quick visual check on the farm and machine status:
7) Reconnect SharePoint to the OWA farm. Run the following PowerShell on the Central Administration server:
Also make sure you test from a browser using a NON-Service account otherwise you might find some errors/unexpected behaviour.