Set older kernel as default grub entry

First, make a backup copy of /etc/default/grub. If something goes wrong, you can easily revert to the known-good copy.
 
sudo cp /etc/default/grub /etc/default/grub.bak

Then edit the file using the text editor of your choice (e.g. gedit, etc.).
 
sudo -H gedit /etc/default/grub

Find the line that contains GRUB_DEFAULT - this is what you'll want to edit to set the default. You must know the full name of the kernel you want - e.g. Ubuntu, with 
Linux 3.13.0-53-generic - along with the full name of the "advanced menu" - e.g. Advanced options for Ubuntu.

To list all kernels do:
 dpkg --list | grep linux-image

You then combine those two strings with > and set GRUB_DEFAULT to them as:  

GRUB_DEFAULT="Advanced options for Ubuntu>Ubuntu, with Linux 3.13.0-53-generic" (including quotes).

Save it, then build the updated grub menu.
sudo update-grub 

Sources:
https://askubuntu.com/questions/216398/set-older-kernel-as-default-grub-entry
https://www.cyberciti.biz/faq/howto-display-all-installed-linux-kernel-version/