Navigate to Applications > Adobe Lightroom > Uninstall Adobe Lightroom and double-click the "Uninstall Adobe Lightroom" executable:
- On the Start menu select Settings.
- In Settings, select System > Apps & features.
- Select the Adobe Lightroom, and then select Uninstall.
- Follow the directions on the screen
Alternatively, if you are using Lightroom CC 2015, you can uninstall using the Creative Cloud desktop app following these instructions: Uninstall or remove Creative Cloud apps
Download install Lightroom 2015.0/6.0 using the application installer here: https://helpx.adobe.com/lightroom/kb/lightroom-downloads.html
Note: The installer on this page works for both the perpetual version of Lightroom 6 as well as the Creative Cloud version of Lightroom CC 2015.
If you receive a message that says “This update is not applicable to you”, you’ve missed step 2. The base 2015.0/6.0 release must be installed before attempting to install the update/patch.