Click Start Import next to the WordPress importer.
Drag your .xml file into the box, or click the box to browse to the file on your computer.
Once the file has finished processing the uploaded file, click the Start Import button. You will be asked to reassign the authors of the imported items to an existing user on the new site before starting the import process.
Note, if you had more than one author on your site and wish to keep your content assigned to the same authors: invite the user to your site on WordPress.com prior to import. This will allow you to assign the posts to the correct author. Inviting the users will require they have a WordPress.com account.