Thanks for trying Mylenium, but it didn't work.
As I said in my post CS6 Extended doesn't show up anywhere as an installed programme, and even CCleaner can't find it. This means that I can't remove the CS6 Trial before running the tool. I did run the tool anyway selecting CS6 as the object to be removed, the tool ran, reported success but my CS6 still opens as the Extended Trial.
Even opening CS direct from the file gets the same result. I am tempted to just de-install both CS6 files and try to re-install CS6 but I am not sure of the result.
Tried running the tool again, this time selecting all the cs5, 5.5, and cs6 to be removed. the tool ran and reported success.
The cs5 and cs6 folders were removed OK.
I re-installed cs6, which went normally and my licence was accepted during the install.
However, cs6 still opens as a cs6 Extended Trial and, once again does not show up in the installed programmes list of the control panel or CCleaner.
Moving discussion to the Licensing forum.
After a thirty minute on-line chat with a support tech I was told that the problem was too complicated and that I would have to ring another number when the experts open up on Monday.
I removed the CS5 and CS6 folders from the C:\programs folder, and ran the Cleaner again.
Re-installed CS5 and activated it then re-installed CS6. The installer suggested the wrong serial no for CS6 at first, but when I corrected this the programme installed correctly, and now opens correctly.
Puzzling because I have never used a trial version of CS5 or 6.
I know the OP solved his issue already, but thought I'd post my answer too since I came across this while looking for one.
Instead of uninstalling/renistalling... I just accepted the path it was trying to take me down to buy CS6 extended. And when it asked me for my serial, I just put in my CS6 serial. I had already done this before, when I installed it. But I did it again anyway. Thus, Extended no longer loads asking to purchase after a trial. Just normal CS6 comes up. If that messes up my serials available for installation, I'll cross that path when I come to it
Yep, that's what I did too...worked for me.