-su zimbra
-zmcontrol -v (write down)
-zmcontrol stop
-do a backup (copy ENTIRE /opt/zimbra and any symlinked/mounted directories/folders-try to keep permissions intact)
-
download the Network Edition (as close of a version as you can find), unzip it in /opt or wherever
-./install.sh (you should get prompted if you want to upgrade from an existing version of Zimbra (obviously choose yes)
-follow prompts/instructions, new license end's up in
/opt/zimbra/conf/ZCSLicense.xml (you might have to put it there manually)