i have an ubuntu desktop 11.10 64 bit upgraded from 11.04, with kernel 3.3.0 generic installed from packages. I plan to upgrade automatically to 12.04 LTS. I saw in the release info that the official kernel will be 3.2 (which is the stable one). Will upgrading "downgrade" my kernel? Is it actually possible to perform this upgrade?
Ubuntu never replaces a kernel with another one, all kernel versions are installed parallel, so you can choose which kernel to boot in GRUB.
Before the upgrade, you should make sure the linux metapackage is installed, it always depends on the latest official kernel for your Ubuntu version. I would also recommend to uninstall your custom kernel and perform the upgrade with the 11.10 default 3.0 kernel.
After the upgrade, check this, here you can get the 3.3 kernel for 12.04. Please note that the official 3.2 kernel from 12.04 backports things from 3.3, so if you need some new drivers etc. first try the 3.2 kernel before upgrading to an newer unofficial kernel.