Install a fresh copy of Joomla without any of the sample data.
Then find and download the JConverter extension for Joomla.
Install JConvertor into your new Joomla site.
You'll need to go into your WordPress files and access wp-config.php. Open that file and you'll need to make note of the following details from the file:
1. Database name
2. Database user
3. Database password
4. Database host
5. Database prefix
Go back to your Joomla site and go to Extensions > JConvertor > Global Configuration and enter the database infomartion you just collected.
When that data is in place, click Save and then click Start Conversion!
You'll now see a screen like the one below. It will show the status of all the imported data:
Now you can go to your Article Manager, Category Manager and User Manager to make sure that all the data has been imported successfully.