Sources are released under the CCDL license. (why ?)
BigMuscle's DLL files are not provided in the same archive so you'll have to download them separately.
Upgrading from a previous version :
Use the button in bottom right corner of AGTweaker to delete the previously installed DLL.
It will probably disable glass and say that's still in use, so restart your computer (with glass disabled), re-launch AGTweaker and press this button again.
It should then display "Successfully deleted" and you'll be able to install the new version properly.
Aero Glass Tweaker GUI for Win8 v1.3.2
in Aero Glass For Windows 8+
Posted
So, where to download that .dll file ?