While I have not spent much looking, I have yet to find a way to have Ubuntu 10.4 manage the number kernels it keeps after upgrading. I have had to manually remove older kernels to apply updated versions later.

To list your currently install kernels:

From a Terminal session enter the following:
sudo dpkg -l | grep linux-image | more

To remove kernel packages, enter the following:
sudo apt-get remove linux-image-2.6.xx-yy-generic

Note: You can remove multiple installed kernels by just adding them to the list:
sudo apt-get remove linux-image-2.6.xx-yy-generic linux-image-2.6.xx-zz-generic

To list all installed packages:
dpkg --get-selections

To list all files a package contains:
dpkg -L packagename

To install a package:
dpkg -i packagefilename
For example:
dpkg -i somepackage.deb

To list available packages:
apt-cache search –names-only ‘stringtosearch’

To clear apt cache:
apt-get clean

To upgrade one software package:
apt-get install –only-upgrade packagefilename