You don't say whether it's NE or OSS version, not that it makes much difference. Please update your
forum profile with the output of the following:
There is no great difficulty in doing a migration but do you actually mean an upgrade or are you moving to a new server? For an upgrade you must backup your /opt/zimbra directory and then run the install.sh and it upgrades your system and retains all your configuration and users. For a migration it's slight more complex, please search the forums and
wiki for further options and details.