If you use grub and have a boot menu with several different entries, did you know you can configure KDE to let you pick which one to use when rebooting?
Go to System Settings and on the Advanced tab, pick Login Manager. On the Shutdown tab, pick Grub as the Boot Manager.
That’s it. Now when you see a restart button it will have a little arrow that will allow you to pick any of your grub entries for the next reboot only.