There comes a list of differences between the two versions Creator 2.0 and 2.1, so it can be much easier to follow up all the changes where some of them are not visible in a menu or tab at first sight.
2.0 and 2.1 are co-existent, that means you can use both at the same time, but you should avoid accessing the same project with different versions because the internal structure of a project differs. Having saved a project under 2.1 it may not be opened again with 2.0 although there has a backup been created (when opened with 2.1) from which you may re-start with 2.0.
Updating components for a project overwrites the PROJECT's components, not those in your component list.
Not updating components will leave your project as-it-is with the older versions.
Bit I would always suggest to use the latest version of a component, sometimes there are nasty bugs removed. Have a look into the according datasheets, there (at the very end) is a list of changes made so far.