There was a hidden folder called BT Windows that I deleted. It still didn’t give enough space, I ended up doing a full reset of the PC. Thanks for your help. This should become a job for someone, finding out how to resize the Android partition and Windows.
I had the same problem as I had installed a few applications before making the update 1511 and he said me there was not enough space.
I therefore redid a clean install of windows 10 from this image (without loosing the activation) : http://techtablets.com/2015/11/teclast-x16-power-and-pro-international-windows-10-image/
and I installed the update before installing something other. I then erased the old windows. It remained about 30 G on the C: drive. I install now programs on the C: drive and my applications on the SD card.
I know i am not responding to subject of the topic (sorry) but I have a problem with the Location Setting on my android OS on the X16 Power. Its pissing me off as no map app will recognise my current location. Its seems to work fine with windows 10 (even though location is not 100% accurate). I would really appreciate if you had any suggestions in fixing it.