When I bought Thesis, I had a heck of time installing it because I had to piece together the how-to information. In the name of saving others some time, here's a step-by-step tutorial that even a newbie should be able to follow:
After you download Thesis, it will unpack a folder named Thesis_18 (or whatever the latest version is that you bought).
Open it. (Leave the zipped file alone.)
Look for the file labeled Content-Sample.
Change its name from “Content-Sample” to “Content”.
Store the Thesis_18 folder on your desktop.
Go to your host site and log in.
Go to the C-panel and scroll down to the Files section.
Choose “Unlimited FTP”.
Java will load the FTP client. You’ll see two boxes—one on the left with a list containing Desktop, My Documents, Network and My Computer.
Click on Desktop. Highlight the Thesis_18 folder, but don’t click on it.
In the box on the left, click on and open Public_HTML.
Click on the name of the domain you plan to use your Thesis theme on. Scroll to the WP-Content folder. Open it.
Highlight the Themes folder.
Click on the arrow that points from the right box (in which you’ve already highlighted the Thesis_18 folder) to the left box, and the FTP client will load the Thesis file into your themes. It will take a few minutes.
Go back to the C-panel.
Go to the File Manager icon and open it. You’ll see four choices. Choose the Web Root (public_HTML) option. Under the four choices, make sure that the proper domain name is selected. Click “go.”
Choose the proper domain name from the list you now see. Open it.
Choose and open WP-Content.
Choose and open Themes.
Choose and open Thesis_18.
Choose and open Custom.
In the toolbar, click on Change Permissions.
Click in the empty box next to Write, under Group. This will insert a checkmark and change the three numbers underneath from 755 to 775. Click on Change Permissions.
Unhighlight Cache by clicking on it.
Highlight Layout.css. In the toolbar, click on Change Permissions.
Next to Read and Write, click on all three boxes so that they all have a checkmark in them and the numbers at the bottom have changed to 666. Click on Change Permissions.
Log out of your host site and go to the admin page of your blog. Go to Appearance and click on Themes. When it opens. Thesis should show up as one of the theme choices. Activate it. You’re done! Well, except for the part about designing the site. Enjoy!