Unneeded kernel image shall to be removed.
Find out which images are installed
# dpkg -l | grep linux-image
Message (example)
ii linux-image-3.2.0-2-amd64 3.2.9-1 Linux 3.2 for 64-bit PCs
ii linux-image-3.2.0-3-amd64 3.2.21-1 Linux 3.2 for 64-bit PCs
ii linux-image-3.2.0-4-amd64 3.2.32-1 Linux 3.2 for 64-bit PCs
ii linux-image-amd-64 Linux 3.2 for 64-bit PCs (meta-package)
Which image is active?
# uname -r
Message
3.2.0-4-adm64
Remove an image (example)
# apt-get purge linux-image-3.2.0.2-amd64
Grub will be reconfigured, but for the safety:
# update-grub
If you try to remove the image which ist currently in use , a message will appear. The process then can be canceled.
If you removed the wrong image, You can reinstall it. Do not shutdown Your computer until the image is reinstalled.
Example:
# apt-get install --reinstall linux-image-3.2.0-4-amd64