Dissertation: How to properly reference earlier versions of working papers in the German academic system? I recently became the co-author of a working paper an older version of which is online (at which stage I was not a co-author yet).

We added and changed most of the content, however some applications remained virtually unchanged. How do I need to cite/reference the earlier version of this paper to avoid plagiarism concerns? We already added "An earlier version of this paper circulated as old paper name".

I do my PhD in Germany. How do I need to cite/reference the old working paper to avoid any plagiarism concerns?

Based on the comments: 


The earlier version of the paper was not pubslished in a book/journal, but posted online on SSRN. 
I am not worried about how journals perceive an evantual submission, but merely about the (german) academic regulation(s) regarding plagiarism.
What I typically did in such a case was either a footnote at the title in the gist of


  A previous version of this paper appeared at XYZ Conference in 1201.


or a mention in the introduction with the citation


  This paper is based on our previous work [ABCD+ '01].


Two side notes:


If this is a paper and you submit double-blindly, you'd need to revise the statements accordingly. You might even want to remove them for review and/or inform the editor.
The information on previous versions and an explanation "what's new" belongs into the cover letter of a journal submission.