Nope. There is no 'promote to master' function in NBU.
You will need to remove existing NBU installation on the media server, change the hostname to match the master server name, re-install NBU as Master and patch to same level as before, then perform a catalog recovery (as per the steps listed in the Troubleshooting Guide).
You would be better off providing a new server, or have a 'standby' system ready or else cluster the master server. Unfortunately only new master server installations can be clustered or with assistance from a Consulting Partner.
