AUsampler on garageband

You have a software instrument track selected, when you try to enable the AUSampler? If not, create a new software instrument track.

In the plug-ins brick you have to pick the top-most item (the sound generator) to change it to the AU Sampler.

Then you should be seeing these items:

When you hover the pointer over the first item in the list of plug-ins, you should be seeing a menu at the right end "v^". Click the up-and-down arrow to reveal this menu.

When I try to click on it I get nothing to pop up. Is there a specific way you have to click it?