multiple ways to achieve it.
1. export it as ovf and upload it in new vcenter.
2. share the new vcenter storage to the host you want to retire. migrate the vm to the storage and add it in to the inventory where you want to run it.
3. migrate the vm to other datastore (removable disk) and upload in to the new vcenter enviornment.
This 3 i can remember right now. there are much more in different scenarios.
Thanks for the swift response - how do you export it as OVF? Does it need to be powered down to see that option?
Yes, the VM needs to be powered off. Once done select the VM, click File -> Export -> Export OVF Template.
If you want to minimalize downtime I suggest to use Veeam or another backup product.
* Keep the VM powered on
* Do a full backup of the VM to some NAS / CIFS storage
* Shutdown the VM
* Do a incremental backup (it will take just a few seconds / miutes)
* Restore the VM on the other side
Point with this approach is that you save 50% of the total downtime.
Another possibility is to use replication with Veeam - you can minimalize downtime to almost zero.
Downtime is not an issue - it's a backup DC.
Then use export / import OVF. It is the simplest way.