Basically, to shrink your partition you'll need a
LiveUSB boot to do that, because otherwise those partitions would be mounted and in-use (locked).
After you've shrunken your partition, and set-up a new one for
Windows (do it carefully as shuffling/resizing partitions after an install is just a pain and can get risky), you can install
Windows safely without losing your
Just make sure you don't let the Windows installer overwrite/format/delete any of your
Kubuntu partitions in the process.
Windows is installed, the
MBR of your hard-disk will be overwritten, thus deleting
Grub. And you won't be able to boot into
Kubuntu. This can easily be fixed though, through yet again a
You can check out this guide to find out instructions to restoring
As always, read up instructions before doing anything. If you're not sure about something, Google for step-by-step instructions, read it, then ask new questions :)