You have to follow the below steps

http://codex.wordpress.org/Changing_The_Site_URL (Use the Redirect Method in this link)

http://yoast.com/move-wordpress-blog-domain-10-steps/

Inform Google via webmasters tool

Update Analytics Code (http://www.koozai.com/blog/search-marketing/how-to-change-website-domain-in-google-analytics-9918/)