I created a new page by copy an existing one. Trough the properties I was able to change the title, but unfortunately not the name of the page, I have the wrong pagename in the URL as well. How or Where can I change the name of a page? Thank you in advance!
As @Ritesh_M correctly answered: please use the "Move" operation of the AEM authoring user interface. It will give you the possibility to rename the page as desired.
However, I do not agree with @Ritesh_Ms second option: moving nodes in CRX DE has a couple of downsides.
First of all, this is a regular authoring activity, so there is no need at all to refer to development tools such as CRX DE.
Additionally, the AEM authoring UI will take care of a couple of other aspects when moving, deleting or renaming pages, such as reference updates (e. g. if you linked to that specific page from another page) and also handling publication/depublication and reflecting the right state of the page on the publish side (if the page has been published before renaming/moving it). If you rename nodes on repository level (e. g. through CRX DE), these actions will be skipped.