When your computer first begins to boot, at the GRUB screen it should show Windows 7 listed below Kali. You have to use the down arrow until Windows is highlighted, then hit enter. All Linux distros set themselves to be the default OS, but you should have about 10 seconds to select Windows (or other OS's).
In some cases, if you do not see GRUB, you may have to watch carefully at boot to see what key to press to get "Boot Options". These usually show up in one of the corners of the screen, or at the bottom, and it may be ESC, or any of the F-keys, like F1, F2, F10, F11, F12.
Hopefully one of these methods will work for you. Good luck!
