You have two options:+ modify the grub configuration and reflash the libreboot. That's too much hassle for a small thing like that.
+ modify /vmlinuz and /initrd.img soft links to point to your new kernel.
To save you some time: you should upgrade to the latest 3.10.x kernel. The kernel from 3.11 on have introduced a bug into the graphical chip driver. So there will be no pretty graphical interface with any of those kernel.
