I'm not with Laminar Research, just a fellow simmer in the UK, but presumably you already have a valid copy of X-Plane 11.30 purchased from Laminar Research and you are simply trying to update it further, I guess to 11.31?
Presumably also, when you try to do this, you get a 'Permission Denied' message?
If this is correct, it may be best to post a copy of your X-Plane Installer Log.txt file, so that others on this Q&A forum, more knowledgeable than myself can have a look and assess what the problem may be?
If you're not sure how to upload a copy of said file to this forum, please click on the following link, which will show you some slides that I've put together and hopefully guide you through the process:- http://questions.x-plane.com/?qa=blob&qa_blobid=11708571559817895598
If you purchased your X-Plane 11 copy from Steam, then please visit their discussion website @ https://steamcommunity.com/discussions/