You can install a kernel manually by downloading it from the sourceforge project page, under the Files header, Kernel section. Just pick one and download it.
[url]https://sourceforge.net/projects/freeghost/files/Kernels/[/url]
Once you download it, backup the existing kernel and move the one you downloaded.
[CODE]
sudo cp /tftpboot/fog/kernel/bzImage /tftpboot/fog/kernel/bzImage.backup
sudo mv [downloaded kernel] /tftpboot/fog/kernel/bzImage
[/CODE]