From your VNC Console screen:

• Reboot your server via the CTRL + ALT + DEL button on top of the VNC Console screen or by pressing the Reboot button in your dashboard. If rebooting via the Reboot button, your connection to the VNC Console will be disconnected as the server reboots. While you have the VNC Console popup window selected, keep refreshing it with the F5 key until your get reconnected.
• From the boot menu select a different kernel and hit Enter
• If you do not see a kernel selection menu, and instead your server immediately boots up into the operating system, follow the first step above, and make sure as soon as you are connected to the server via the VNC Console, hold down the left SHIFT key. This will case your operating system to show the kernel selection menu.