The method used to convert the sample rate of audio files also applies to Apple Loops.
Select an Apple Loops file in the Audio Bin.
Do one of the following:
Choose Audio File > Copy/Convert File(s) from the Bin’s local menu bar (or use the corresponding key command).
Control-click (or right-click) the Audio Bin, and choose Copy/Convert File(s) from the shortcut menu.
Choose a sample rate (and all other file conversion settings) in the ensuing dialog, select the folder location, then click Save.
The file is converted based on the originally recorded tempo and key of the Apple Loops file—not the tempo and key of the project.
Note: If a new Apple Loops file is created, it needs to be indexed to make it visible in the Loop Browser. Loops can reside in any directory, but you need to tell Logic Pro where to find them.
You will probably not need to convert Apple Loops as often as standard audio files when working with Logic Pro, as Apple Loops offer a major advantage: if the sample rate of your project is changed, the playback speed of all Apple Loops currently used in the project is automatically adapted to the newly selected sample rate.