Help with Removing a DC role from a Server 2003.

I have 2 DCs in my network. One is a Server 2003 and the other is a Server 2012 R2. They are co-domain controllers. I want to demote the 2003 Server from the DC role and then to remove from my network. 

Steps Taken so Far: I checked and found out that the Server 2012 R2 is the PDC. 

Can you please give me the correct steps and [checks I have to make before] to demote the Server 2003 from a DC first? Then I will remove this server from the network.

Thanks for you help.