Even if you can upgrade this theme relatively easy with “Easy Theme Upgrade”, the many customizations I made in CSS and on the pages, make that this has to be done very careful. I also want to experiment with HTML and CSS in the new version of the theme, so no fast upgrade there. Upgrading WordPress it self also requires careful supervision. This site should not brake down because things are not as the new WordPress expects it to be.
Between learning new tricks and thinking about ways to use them, it will take some time for the update. Normally I do not need much time to learn new stuff, and using it immediately makes it stick better. So let us hope, that other circumstances allow me to do this within the first weeks of this new year (set apart things like a new job or a course, which are circumstances with a much higher priority, than this site).