you can't really hot swap the kernel, because all of the system runs on it.

you'd need to stop the system (you can save its state and recover where you left), reboot to load the new kernel and let it take control.

however, there are some distros and programs that allow you to hot swap certain parts of the kernel (mainly drivers) without rebooting. Note that, even though the system doesn't reboot, most packages still need to be restarted for them to pick up the new driver.