To use an ACR preset, you need to get it into the Presets tab. The easiest way of doing this is by copying the preset files into the folder on your computer. Here's how:
1. First, after your purchase, download and unzip the file to your computer.
2. Then, navigate to the folder where the presets are stored:
Username/Library/Application Support/Adobe/Camera Raw/Settings
(If you don't see the Library folder, do the following: Open up the Terminal application on your computer, and enter the following text: chflags nohidden ~/Library/, then click the Return key).
(If you don't see that location, then you'll need to make sure that your "Show Hidden Files..." setting is turned on. To do this, go to the Control Panel > Appearance and Personalization > Folder Options > Show Hidden Files and Folders. Then, in the the View tab, change the default setting of "Don't Show Hidden Files, Folders and Drives" to "Show Hidden Files, Folders, and Drives" then click the OK button.)
3. Once you have this folder opened, locate the download folder with the presets and open this folder in a separate window. Then, drag the .xml files over to the Settings folder. (You need to be sure that you DO NOT add additional folders to the settings folder; ACR does not support sub-folders.) Here's what your folder will look like when you're done:
4. Now, open up an image into Adobe Camera Raw (close and re-open it if you already had it opened). Click on the "Presets" tab near the top-right and your presets will be added to the list: