Moving from test environment

Hello,

I have been developing site in a subdomain "test.maindomain.com". Now when the site is ready I want to move to "maindomain.com". It is literally copied files to another domain. What is the best way to do that? to transfer site from one domain to another?

One more thing. It is a multisite installation. I allow my users to create their own blogs. It was working ok but last few users gets this message:Table 'saharatr_test1.wp_17_fm_settings' doesn't exist. I get the email to my admin inbox that new site has been created but when I want acces the site I get this message.

Thank you,

Stuart