To remove a node from a Proxmox cluster you will need to SSH into any node other than the one you want removed.
Next, identify the name of the node you would like to remove from the cluster with the following command:
pvecm nodes
Next, SHUTDOWN THE NODE TO BE REMOVED.
Next, remove the node with:
pvecm delnode NAME_OF_NODE_TO_BE_REMOVED
Should you encounter the following error:
cluster not ready – no quorum?
Fix with:
pvecm expected 1
Then run the following again:
pvecm delnode NAME_OF_NODE_TO_BE_REMOVED