Maybe I am asking for something so obvious, that no one has explicitely written before.
What should I do to have a new editor working?

I have XOOPS 2.5.1a and AMS 3.0 and I am trying to add FCKeditor 2.6.6 available from xoopseditorsALL package.
As I understood descriptions, all I have to do ist to copy the fckeditor directory into /class/xoopseditor.
I did so but I can't see the new editor neither in AMS admin page nor in Module config options page.
What is missing and how can I verify that a new editor is correctly installed?

It's so simple - just have to reinstall (update) the System module
(the list of editors is created from xoops_version.php, which is processed during module installation; it is created based on directory listing of /class/xoops/xoopseditor).

Now I start verifying that new editor really works in commens and modules.