Remove Old Linux Kernel, Clean Up Boot Menu

Each time when Ubuntu updates to a new Linux kernel, the old one is left behind and the boot menu gets longer. If your new Linux kernel works well, it's safe to remove the old one and clean up the boot menu. Do take these steps carefully as incorrect removal of the items can make your system unbootable.

1. Go to Applications (or Main Menu) > Accessories > Terminal.
2. Enter uname -r to print the Linux kernel version you're running (e.g. 2.6.32-22-generic).
3. Go to System > Administration > Synaptic Package Manager.
4. Click Status from the left panel and select Installed.
5. Enter the main version number (e.g. 2.6.32) in the Search box.
6. Right-click the items with smaller sub version number (e.g. 2.6.32-21) for older Linux kernel and select Mark for Complete Removal. The files for the older version to remove may include linux-headers-2.6.32-21, linux-headers-2.6.32-21-generic and linux-image-2.6.32-21-generic.
7. Click Apply from the top panel.
8. 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.

Change Default Boot Options

After full installation, Ubuntu is set to be the default operating system to boot up if no key is pressed within a few seconds on a multi-boot system. You might want to set your preferred operating system to boot up by default. This can be done easily with StartUp-Manager.

1. Go to Applications (or Main Menu) > Accessories > Terminal.
2. Enter sudo apt-get install startupmanager(or copy the highlighted code and press Ctrl-Shift-V to paste it in the Terminal).
3. Enter password used upon installation of Ubuntu.
4. Go to System > Administration > StartUp-Manager
5. Enter the same password to perform pre-configuration tasks, which include searching bootloaders to operating systems.
6. Select the default operating system from the pull-down menu, click "Close" to perform post-configuration tasks.

With StartUp-Manager, you can also do others such as manage Usplash themes, adjust bootloader menu resolution or set timeout in seconds. Avoid changing timeout to 0 seconds if you need to select a system to boot up from a multi-boot menu.