With Windows Server 2012 R2 and later DHCP failover is very easy to configure. DHCP failover can also make it easy to move DHCP from one server to another without loosing the current leases. If you have a large network you will need to remember to update your DHCP helpers/relays if there is an IP change.
To migrate DHCP failover from servers A and B to servers B and C;
Verify that all failover scopes are replicated on servers A and B.
Deconfigure failover on server B, this will remove failover and the associated scopes from server A.
On server B, delete the previous failover relationship with server A.
Configure failover on server B with server C as the partner.
Continue this process if you need to migrate DHCP failover from servers B and C to servers C and D.