To import from a WordPress export file (WXR) into a WordPress blog follow these steps:
Log into that blog as an administrator.
Go to Tools ? Import in the blog’s admin panels.
Choose “WordPress” from the list and click the “Install Now” button in the modal window for the WordPress Importer plugin.
Activate it by clicking the “Activate Plugin & Run Importer” link.
Upload your WXR file using the form provided on that page.
You will first be asked to map the authors in this export file to users on the blog. For each author, you may choose to map to an existing user on the blog or to create a new user.
WordPress will then import each of the posts, comments, and categories contained in the uploaded file into your blog. In addition, you can import attachment by checking the “Download and import file attachments” option.