You didn't define "it doesn't work" so it is hard to know what your problem is. Most people forget to change the links, which is usually done with a Search and Replace plugin.
As I say, the first two references I gave in my previous post really go through the process in fine detail. If you are just moving from /new/ to the root of the domain, http://codex.wordpress.org/Giving_WordPress_Its_Own_Directory#Using_a_pre-existing_subdirectory_install is probably the best approach.