I am in a bit of a quandry. My boss uses Lightroom 5. I have used Lightroom 5 until my PC had issues. Now I have Lightroom 6 CC 2015. Which I love, but I can't use it for work. I need to go back to Lightroom 5. I found where I can install it, but it needs a Serial Number to launch. How can I revert back to Lightroom 5 until I can convince my boss to upgrade?