title: Protocol Buffer: Version Change
body: <p>I have accidentally installed version 3.0.0 and most of my files naturally gave tons of errors. Now I want to take it back to 2.6.1. I already downloaded 2.6.1 and installed, however when I do <code>protoc --version</code> it still shows <code>libprotoc 3.0.0</code>, which is wrong. </p>
  
  <p>Is there a way to set the version to 2.6.1 or is there a way to uninstall 3.0.0? </p>