Check you launching from the correct shortcut, as when I installed it on my Mac it left the Lightroom 5 install on the machine, meaning I could launch either 5 or CC 6.
are you mac or windows
if you are using mac please go to application folder and choose adobe Lightroom
if you are using windows got to C:\Program Files\Adobe\Adobe Lightroom and double click on the "lightroom.exe"
How to install LR 6 CC : I suggest going to Laura Shoe's site and she has a very clear video for both Mac and PC
She will relate how you need to tell LR 6 which catalogue to open plus all kinds of other helps.