From easier (1) to the more difficult (3):
- 1) Click on System > Administration > Update Manager > Click on Check button > Apply all updates including kernel.
- 2) Use Synaptic, search for linux-image and select the generic kernel version you want to install (i.e. linux-image-2.6.xx-yy-generic).
- 3) Compile|the kernel.
Roll-back and uninstallation
You can roll back by selecting the previous (old) kernel at the boot menu and then uninstall the (new) not working kernel. With Synaptic you can uninstall previously installed kernel packages.