Also, remember the port flow:

• client to relay source udp-68 to udp-67
• relay to server udp-67 to udp-67
• server to relay udp-67 to udp-67
• relay to client udp-67 to udp-68

In plain English.

Assuming you are moving DHCP from DC1 to DC2

On DC1

• Open terminal
• netsh
• DHCP
• server \\dc1
• export c:\w2k3DHCPdb all
• Copy to dc2

On DC2 (Assuming it is Server 2012)

• From within Server Manager, select Add roles and features
• Select Role-based of featured-based installation and select Next.
• On the Server Selection window, leave the default and select Next. When the Server Roles window opens, select DHCP. Select Add Features in the pop-up window, then select Next.
• Once the DHCP install has been completed, select DHCP located in the Server Manager dashboard
• Right click the designated DHCP server in the services pane, then select Stop.
• Delete the DHCP.mdb file under the folderC:\windows\system32\DHCP.
• Return to DHCP located in the Server Manager dashboard
• Right click the designated DHCP server in the services pane, then select Start.
• Right-click on the bottom left hand side of the desktop screen to invoke the admin menu
• Select Command Prompt (Admin) to open the cmd prompt using elevated privileges.
• netsh
• DHCP
• server \\Name or IP Address
• import C:\w2k3DHCPdb
• Close the command prompt when completed.

Simply setup your scope options for your new Windows Server 2012 DHCP server and then Authorize it within your domain and the migration is complete. (The GUI should give you a prompt on what to do)