Whenever Ubuntu updates to a new Linux kernel, the old one is left behind and the boot menu gets longer. If your new Linux kernel is working fine, then it is safe to remove the old one and clean up the boot menu.
- Go to Applications (or Main Menu) > Accessories > Terminal.
- Enter uname -r to print the Linux kernel version you are running( example 3.11.0-12-generic )
- Go to Synaptic Package Manager. Menu option may vary depending on the version of Linux and desktop used.
- Click Status from the left panel and select Installed.
- Enter the main version number (e.g. 3.11.0) in the Search box.
- Right-click the items with smaller sub version number (e.g. 3.11.0-10) for older Linux kernel and select Mark for Complete Removal. The files for the older version to remove may include linux-headers-3.11.0-10, linux-headers-3.11.0-10-generic and linux-image-3.11.0-10-generic.
- Click Apply from the top panel.
- Click Apply again from the pop-up window to confirm removal of the marked packages. The boot menu will be cleaned up automatically after the removal is confirmed.
Do take these steps carefully as incorrect removal of the items can make your system unbootable.