If you want to remove entries with old kernels from your Grub menu, remove the kernel and the Grub entry will be removed as well.
How to remove old kernels- Go to Terminal and paste the following command: uname -r
It will print the version of the Linux kernel you are running, this is the one you want to keep. It should look something like this: 2.6.31-16-generic.
- Go to System -> Administration -> Synaptic Package Manager
- Paste "linux-image-" (without quotes) into the search box of Synaptic Package Manager. The results should show every available and installed kernel. A green box on the left indicates that the package is installed.
- Once you have located an old kernel, right-click on it and select "Mark For Complete Removal". Repeat for every kernel that you want to remove (make sure to leave the current kernel!!!) and click the Apply.
Please note that you need to be very careful with what you remove. Do NOT remove your current kernel, or anything that is not a linux-image. It is possible to break Ubuntu otherwise!
Your computer and Grub menu should now be free of old kernels.