Both approaches will work. Safest is just to install Lightroom Classic from the creative cloud app. Run it and point it to your Lightroom 6 catalog. It will upgrade the catalog for you and save a new copy. Then if you confirm everything works right, you can delete Lightroom 6. Make sure you do not fall for the confusing Lightroom Desktop app in creative cloud which is a completely different program altogether. It is a port of the mobile OS version of Lightroom to Desktop operating systems and misses most of the features you are used to from Lightroom 6. You need Lightroom Classic which is the evolution of Lightroom 6.