title: How to change Xcode sdk compiling version
body: <p>I have tried to build an app through to the AppStore but they rejected it due to the app using sdk 11.4. Stating that it needs to use the updated version of 12.1. 
  The current Xcode I have installed is 10.1 or 10B61 which is the latest without making use of a Beta. I have searched through the settings trying to find how to update the sdk as well as maybe target that newer base SDK.</p>
  
  <p>Things I have tried:</p>
  
  <ul>
  <li>Searched for newer Xcode (stated above)</li>
  <li>Searched through settings for the base SDK version number so it can be changed.</li>
  <li>Went to AppStore to find any updates for Xcode (there were none)</li>
  <li>Tried googling how to change/update the sdk, but none give an explicit answer on where this can be done. It merely states that Xcode 10 should come with a base SDK of 12.1, but that does not seem to be the case here.</li>
  </ul>
  
  <p>Please note that this is not to target the minimum version. I know where that is and it is set accordingly. No issues there.</p>
  
  <hr>
  
  <p><strong>EDIT:</strong></p>
  
  <p>I have run $> xcodebuild -showsdks and it shows that sdk 12.1 is the sdk that is installed.
  However, it seems that it is somehow overriding it to 11.4 when it is trying to build to AppStore. Not sure why.</p>