Q:

Switching from OVH kernel to default kernel without reinstalling Ubuntu

I have a dedicated server hosted by OVH.
When installing the server I must have left the default choice of kernel which is to use the stable/tested OVH kernel rather than the distribution's native kernel.
I have recently switched to using APF firewall rather than UFW and after setting up APF with all my rules and starting it with apf -s I get an output that looks like this:
apf(11291): {glob} flushing & zeroing chain policies apf(11291):
{glob} firewall offline apf(11328): {glob} activating firewall
libkmod: ERROR ../libkmod/libkmod-module.c:1655
kmod_module_new_from_loaded: could not open /proc/modules: No such
file or directory Error: could not get list of modules: No such file
or directory apf(11368): {glob} kernel version not equal to 2.4.x or
2.6.x, aborting. apf(11328): {glob} firewall initalized

I changed a setting in APF called MONOKERN which is described as "Support Monolithic kernel builds [no LKM's]" after finding a forum post explaining that this is needed due to the kernel some hosts use.
Restarting APF with apf -r then produced this output:
apf(22524): {glob} flushing & zeroing chain policies apf(22524):
{glob} firewall offline apf(22599): {glob} activating firewall
libkmod: ERROR ../libkmod/libkmod-module.c:1655
kmod_module_new_from_loaded: could not open /proc/modules: No such
file or directory Error: could not get list of modules: No such file
or directory apf(22703): {glob} determined (IFACE_UNTRUSTED) eth0 has
address 158.69.123.46 apf(22703): {glob} loading preroute.rules
//carries on printing out the firewall rules it is setting up...
apf(22599): {glob} firewall initalized

OVH have said that I can always change the kernel during a re-installation, but I really don't want to do that.
I host a somewhat popular game on my server with around 100 users online at any given time. To take the server offline for a few hours to reinstall the distribution and set everything up again really isn't practical.
Is it possible to switch back to the native distribution kernel for Ubuntu 16.04 without performing a reinstallation, and if so how?

A:

# cd /etc/grub.d
# mv 06_OVHkernel 96_OVHkernel
# update-grub

It will list the kernels, with the OVH one last.   You should have a distribution kernel first, but if you don't, follow @James answer above.
# reboot

A:

For anyone else who stumbles across this, here's how I solved it:
I ran apt-cache search --names-only linux-image to search available images.
Choosing the most up to date Linux image I ran:
apt-get install linux-image-4.4.0-59-generic

I then rebooted the server and ran update-grub.
This swapped the kernel out for a general Linux one without losing me any data or requiring a reinstallation.

