How to install Kubuntu 17.04 in dualboot with Windows 7

Today i tried to install Kubuntu 17.04 in dual boot with Windows 7
I shrinked the disc 50 Gigabytes, put the iso on a USB drive with Rufus and bootet from it in Bios.
It brings me directly to a “linux” desktop with an “install Kubuntu 17.04” icon on it.
So far so good, now my problem :
I cannot select a dual boot mode or make it use the empty space, as shown here

how to proceed further ?