If you have a complete Creative Cloud membership or a Photography plan, you should be able to download and install Lightroom CC 2015 from the Creative Cloud site.
Since Lightroom CC is a new product, it will not show as an update in the Adobe Application Manager. Instead, press the install button next to Lightroom in the Application manager.
If you don't see "install" by Lightroom in the application manager, please first try signing out and back in: sign in and sign out of the Creative Cloud desktop app
I have now downloaded Lightroom CC and it is working.
I had not understood that it was a completely separate programme.
When I subscribed to CC I did not download LR as I had already had LR5 on my PC.
Thank you very much for your help.