In case you want to do this manually, here is how it's done:
1. export WP database (using phpmyadmin -> select database -> EXPORT (use SQL format))
2. copy all content from your current wp folder to the new (using FTP usually)
3. edit exported .SQL file (replace old URL to new URL. ie. old sitename was "www.example.com", replace it to "www.newsite.com" using notepad)
4. create WP database on the new location
5. import previously exported .SQL file into the new location (using phpmyadmin -> select database >- IMPORT)
6. edit wp-config accordingly to the new database, login info
7. login to wp-admin, remove previous author (it will remove all posts which belong to him), or just delete all posts
8. optionally delete wp-contect/uploads folder, it contains all your uploaded media files (check it first if your plugins don't have anything in this folder)
Cheers