Install it and the Aria engine. Then check the Aria site to make sure you have the latest update. It's a bit confusing in that updating the Aria Engine and Aria Player are not the same thing. 

http://ariaengine.com/support/aria-engine-update/

These instructions are not correct for updating the Aria Player. Mine is v 1.872 and works fine. You'll find the latest version of Aria for Garritan here:

https://store.makemusic.com/Downloads/Default.aspx?p=1&_ga=2.64705583.1817054786.1511036802-1529495151.1511036802

This is specific to Garritan libraries used in Logic and other Apple apps in High Sierra only. It does not affect Finale and may or may not affect other non-Apple apps:

https://www.garritan.com/blog/garritan-products-and-macos-high-sierra/