how do I change my instant client from 12 to 11?
First make sure you have the instant client downloaded from the Oracle Website and review this video to see how to install the client
http://www.quest.com/tv/All-Videos/1044396072001/Toad-for-Oracle—Using-Oracle-Instant-Client/Video/
Then see the attached image showing how to select different clients when connecting.
Make sure you are disconnected from every session before you can change the client