Very. Very. Very. Carefully.
Copy the files and the DB to your new domain, then search for ALL instances of Oldomain.
HOWEVER. Do not do a blind replace. You don’t want to replace anything in widgets, but you DO want to replace wp_blogs, wp_sites, wp_posts and SOME wp_options.
@ipstenu
What if i do a blind replace?
You don’t want to replace anything in widgets
If I change the domain name, what’s the need of that OLD ONE?
WordPress uses a feature called serialization. That means that some of your data is stored with the LENGTH of the domain name. If you do a blind replace, you’ll lose your widgets and possibly screw up your media table, making everything invisible. Just don’t. Trust me on that one 😉
A quiet daunting task then… is there any other way to minimize the hassle?
Make sure your old domain is exactly the same length as your new one.
i.e if you go from olddomain.com to newdomain.net, you’re fine. but thisolddomain.com to mynewdomain.com would NOT be okay.
