Some day the certificate for the Office Web App Server will expire.
Can this be done by useing IIS Manager to change this or is Powershell our friend again?
Well first we tried to use the IIS Manager to change this. Sorry, this did not work.
We have to use Powershell like this
set-officewebappfarm -certificate "Your new certificate"
Then we had to reboot the server
Thanks to Chief Consultant Tore Gjønnes who works at EVRY AS here in Norway.