I believe the highest you can promote is to the highest rank within the rank below you, Division ranks excluded. Ex; HR can only promote Standard and Division ranks, BOD can promote HR, Division ranks, and Standard, Governor can promote BOD, HR, Division ranks, and Standard, Senator can promote Governor, BOD, HR, Division ranks, and Standard, etc. Don't quote me on that, as I'm not 100% sure that's how it works, but that's what I've used as my basis.