Transfer "Pages" to "Posts"

Hello WordPress community,

I am intern in a Digital Media company and i have a problem.

I had to manually transfer News from an old website into our WordPress system , but as i was unexperienced and had no knowledge i transferred <b>Manually <b> over 600 Newsarticles , putting the images , links etc..

Now my Project Manager tells me that they have to be Posts not Pages.

Is there any way to transfer them , and doing so avoiding to do the same process again which took me more than a week?

You can see on the image here : http://postimg.org/image/uhi303kff/
I want to transfer my “Seiten” as “Beiträge” if i was unclear.

Sincerely and thanks for taking time to read this 🙂