When you first boot up your machine you should see the grub boot menu. At the grub boot menu choose the older Kernel you want to boot to - Once you have chosen the Kernel you want to keep and you have booted into it
uname -r
will tell you what kernel you are currently running on (measure twice cut once)
dpkg -l | grep linux-image
dpkg -l | grep linux-headers
will tell you what kernels/headers are saved on your system - I will also delete the headers - though they dont take up too much space i still purge them, why have them if I am deleting the kernel?
Be advised that it is important to NOT delete the Kernel you are running i.e uname -r
Deleting these kernel and header entries will make your system unusable
then just delete the ones you dont want:
sudo apt-get purge
I will copy the output of dpkg -l | grep linux-image
to a text document so that it is an un-messy process and i can clearly choose what i want to delete vs save
an example of what the full command will look like:
sudo apt-get purge linux-image-3.16.0-41-generic linux-image-3.16.0-41-lowlatency linux-image-extra-3.16.0-41-generic
sudo apt-get purge linux-headers-3.16.0-41 linux-headers-3.16.0-41-generic linux-headers-3.16.0-41-lowlatency
an example of what the output of dpkg -l | grep linux-headers will look like:
jason@casa-wesella:~$ dpkg -l | grep linux-headers
ii linux-headers-3.16.0-41 3.16.0-41.57~14.04.1 all Header files related to Linux kernel version 3.16.0
ii linux-headers-3.16.0-41-generic 3.16.0-41.57~14.04.1 i386 Linux kernel headers for version 3.16.0 on 32 bit x86 SMP
ii linux-headers-3.16.0-41-lowlatency 3.16.0-41.57~14.04.1 i386 Linux kernel headers for version 3.16.0 on 32 bit x86 SMP
ii linux-headers-3.16.0-43 3.16.0-43.58~14.04.1 all Header files related to Linux kernel version 3.16.0
ii linux-headers-3.16.0-43-generic 3.16.0-43.58~14.04.1 i386 Linux kernel headers for version 3.16.0 on 32 bit x86 SMP
ii linux-headers-3.16.0-43-lowlatency 3.16.0-43.58~14.04.1 i386 Linux kernel headers for version 3.16.0 on 32 bit x86 SMP
ii linux-headers-generic-lts-utopic 3.16.0.43.34 i386 Generic Linux kernel headers
ii linux-headers-lowlatency-lts-utopic 3.16.0.43.34 i386 lowlatency Linux kernel headers