To upgrade the kernel and start the new kernel by default, follow these steps: First, download the new kernel file from the specified FTP address. You can use 'wget ftp://server1.domain10.example.com/pub/update/new.kernel' for this purpose. After downloading, list the files to find the exact name of the new kernel file. Install the new kernel using the 'rpm -ivh' command followed by the new kernel file name. Once the new kernel is installed, verify and edit the '/boot/grub/grub.conf' file to ensure the new kernel is set as the default boot option. This can be done by setting 'default=0' in the 'grub.conf' file, where '0' refers to the first kernel entry (which will be the newly installed kernel if it appears first in the list). Finally, reboot the system to start with the new kernel.