When you upgrade kernel on ubuntu, you will add grub menu with new kernel version. Ubuntu doesn’t remove the old entries. It’s very dirty. Why Ubuntu do this? How to remove it.. Hmm.. after several time browsing to find the solution…I found the best solution for me.
This is my first Grub menu after upgrade kernel:
The best way to remove the older menu, you’ll need to edit the file /boot/grub/menu.lst. You can do this by using Alt+F2 and then typing in the following command:
gksu gedit /boot/grub/menu.lst
Click on run and you’ll get the file open. find “#howmany=all” and change it to “#howmany=1″.
Then run “sudo update-grub” to update changes. Next time, only newest kernel lines will be shown.
If you have more than one OS in your PC (example: Ubuntu and Windows), the tip that I mentioned above is the best way to update GRUB automatically. You dont need to delete any lines (and change the “default” value also) after every time your Ubuntu box is updated 
