Yes, you search (not quick search) in Synaptic for kernel. (You can also do
by looking in Status, Installed and quick seach for linux). Then scroll down
to the L section for linux, look for linux-image and then the linux-image
files with the same version number. The linux kernels that are installed
have green boxes. You can remove old kernels by right clicking and choose
Mark for Removal. Then Apply.

You can also do this safely using Ailurus which is like Ubuntu Tweak. Once
installed it has a section called Clean up and one of the things it does is
remove old kernels. This is easier and the utility has lots of bonuses.

Ailurus is available from Getdeb or from here:
https://launchpad.net/ailurus
http://code.google.com/p/ailurus/