I currently have the trial version of CC Lightroom. Should I uninstall before installing standalone LR6 from disc?
Yes that would be a good practice first to remove the trial version of Lightroom CC and the Creative Cloud desktop application as well if you don't have any other Creative Cloud application to use.
After that you can Install Lightroom 6 either from the disc or the below mentioned link:
Download Photoshop Lightroom
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