I used to be a Sergeant, then I did this awesome post and the rank of Alex Rogan Starshipgunner was given to me. Cause the awesome dripped onto the keyboard like the dew from Mount Olympus, it was so powerful, the dew, that my wife walked by the keyboard and got pregnant. I said, we already have 2 kids, no more, and the egg went back home and the sperm surrendered saying, "sorry Alex Rogan Starshipgunner!"
So if you want your rank to change, be more awesome. But you can't be as awesome as me, I played a video game, was so good at it, aliens came and said BUENO SENIOR! I said, I'll knock this out, give me a few, and bam.
Or you can edit your rank in settings...