Refer to this How to Remove the old (or new) kernels
http://ubuntuhandbook.org/index.php/2015/08/install-latest-kernel-script/
1. In Ubuntu with a graphical interface:
1.1 Installing synaptic Package Manager in Ubuntu Software Center
1.2 Deleting packages using Synaptic Package Manager:
- Click the Reload button in the want to remove the new kernel.
- Select Status-installed on the left pane to make search list clear.
- Search linux-image- using Quick filter box.
- Select a kernel image "Linux-image-x.xx.xx-generic" and mark for (complete) removal
- Finally Apply changes
2. Under the Ubuntu Server environment:
2.1 uname-r Get current kernel version 2.2 Dpkg-l | grep linux-image-
Dpkg-l | grep linux-headers- Gets the name of the currently installed package
2.3 sudo apt-get autoremove kernel_image_name replace Kernel_image_name with the name you obtained in step two to delete.
Be careful not to delete kernel that need to be preserved.
Delete old kernel Linux kernel in Ubuntu