Manually upshifting simply allows the tranny to move to the next higher gear if it is ready to. It doesn't force it to shift if it doesn't want to. Downshifting is quite another matter... :hit: On non-computer controlled trannies like in VN-VP pulling it down a cog or three can make things rev to to moon or worse. Not always the good choice.
If you own a Holden owners hand book, or can get access to one, it describes in great detail how to use, what to do and what not to do with your auto trans...