1- Any option about export the previous vCenter configuration to the new one?
2- For join ESXi hosts to the new vCenter, should I remove them from the old vCenter then add to the new vCenter?
Not required. On the new vCenter server right click and add the hosts.
You can run an upgrade/migration - depending on wether you are currently running vCenter on Windows or a vCSA - from vCenter Server 6.5 to a vCenter Virtual Appliance 6.7, which takes over all settings including the inventory (hosts, VMs, etc.).