You should be able to select "ImageMagick PECL extension". If you cannot select this, you will need to contact your web host provider and ask them to install ImageMagick with PECL.
Installation:
Download Andy-HeaderThumbs-1.8.zip and unzip it.
Copy the src/addons/Andy/HeaderThumbs directory to your server.
From the Admin Control Panel Install the add-on.
Directory preparation:
Create a directory in your web root called /misc/ and set permissions to 0755.