We're remodeling a room with a severely undersized doorway - it is much shorter than the standard 6'8", so much so that I hit my head on the jamb if I don't duck when walking through it.
After demolition, I discovered a "header" (circled in red) with a good amount of empty space between it and the top plate:
It seems to just be toenailed into the king studs on the side, and isn't supported by anything except the thin jamb strips. Therefore, I doubt it is doing much in the way of supporting or bracing this wall in any way.
Can I just remove this "header", and move the jamb to the bottom of the top plate? Or do I really need to install a new header+jack studs? This is a single-floor house, and the only load on this wall is (perhaps) the roof above. It seems to me like the doubled-up top plate and king studs are more than enough to support the load.
A bigger picture: