I have reported it as a bug but I found a quick and fast solution, delete the kernel from boot that doesnt correspond to your device, for example if you have a rpi3b delete the kernel.img and if you have other rpi delete the kernel7.img and you will have space.
You need to go to /boot and do it as admin:
cd /boot
sudo su
(enter password)
rm kernel.img or kernel7.img depending on the device.
Good luck!