Moving from subdirectory and subdomain -> root

If I understand you correctly, you’re removing the old Mambo site and intend to run WordPress as the main site in this domain.

If that’s the case then (depending on any plugins that you have running) all you will need to do after making backups of everything is move the entire contents of your /wordpress directory up to the webroot and run a search and replace on the database for the string ‘dev.domain.com’, switching it for ‘www.domain.com’

Do bear in mind that this last step is thoroughly dependent on the two strings (dev.domain.com and www.domain.com) being the same length. If they are different in length, for example ‘staging.domain.com’ and ‘www.domain.com’, then you may be better served by a tool such as the incredibly useful Search & Replace for WordPress Databases by Interconnect IT