Installing XP9 after demo

I have installed the XP9 demo from the website (I tried XP10 but was a bit too heavy for my elderly PC) and it runs really well, better than FSX or P3D, so I've ordered a copy from Amazon UK.

The demo seems to be a time limited version of the full thing with limited scenery installed. It checks to see if the disc is inserted before starting the clock, so what I'm wondering is will I have to uninstall the demo and then install the full thing from disc, or can I just install the scenery that I want to use (I'll only be flying UK initially) on top of the demo and run it with disc 1 in the PC? That would save some time if possible.

Also, if I later want to install additional scenery from the other discs later, am I able to do this, or do I have to install all the scenery that I'm ever going to use on the initial installation?

Thanks,

Paul