Changing a kernel is a potentially significant change and should only be done if you really need to.
As always, make backups before you make any serious change to your server.
Then, the typical procedure for updating your kernel is as follows:
1) Update your system using the package system.
For Ubuntu or Debian, i use:
For Fedora and Centos:
(see /etc/yum.conf to make sure there is no 'exclude=kernel*' line in the [main] section)
For ArchLinux :
(see /etc/pacman.conf and comment out any line that says "IgnorePkg=linux")
2) Look in /lib/modules for the highest version of installed kernel library available.
3) In the control panel, in a droplet's settings, look for a kernel that matches your OS version, kernel library version, and architecture (x32 or x64). Select that kernel and submit.
If the kernel doesn't exist there, stop and let us know your OS and version, your architecture, and what you saw in /lib/modules in a support ticket.
4) Once the kernel is set, reboot and test.
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