domain name and ip address

I would like some help in changing to domain name on a live website to a new domain name and ip address. I own both domain names. The current domain name www.happypsychic.com. I would like to change it to blog.westcoastmedium.com, with changing any of the current content, posts, files and photos. I just want to change the domain name. Can you please help me with the steps to accomplish this. Thank you rflores