Changine sizes of splitted windows

[Texaner]

Hello,

I am quiet new to emacs. I'm using a splitted window (ctrl + x + 2) for
programming purposes. Is there a possibility to change the sizes of the
windows, I mean moving the middle line that splits the window, only by
keyboard instead of using a mouse?

I tried to look it up in the manual but I was not succesful.

Thank you very much in advance for your answers.