Installing WordPress/Thematic child themes is the same as installing a “usual” theme.
The only difference is you need both the parent theme and child theme uploaded to your WordPress theme directory.
1. Upload a parent theme of your choice via FTP
2. Upload a child theme via FTP
3. Activate the child theme
Download the Thematic theme Framework and extract the zip file.
Take the /thematic/ folder and upload it to your /wp-content/themes/ directory through FTP.
Similar to the previous step, you extract the BT EX/ folder and upload it to the /wp-content/themes/ directory via your FTP client.
Now that you have both the Thematic theme and Thematic child theme uploaded, the final step is to activate the child theme.