That depends on when you created Droplet. In past, Kernels was managed from Control Panel. This was changed some time ago and now it can be updated via Droplet console (terminal/SSH). The only thing is what you need to do is to change from your current Kernel to Internally managed kernel.
After that you should be able to upgrade kernel from Droplet (e.g. apt-get upgrade && apt-get dist-upgrade).

To do it, follow DigitalOcean tutorial on How To Update Kernel

If this is the case, when you update you should see image like this