"How can someone be removed as MOD from a board ?"
Presumably by being a very bad Mod. If you could convince Admin that the Mod in question was making inappropriate deletions, and not acting in a fair manner when moderating the MB, then you could probably get them removed.
Be careful though - on some of the MBs of obvious penny stock scams I moderate, like EGOC, many posters commit countless ToU breaches because they can't get to grip with iHub's ToU, which are actually not difficult to understand or indeed to comply with.
Those who are persistent offenders probably wouldn't want to draw Admin's attention to themselves by complaining about a perfectly fair Mod when their own record is bad.
That could well have unintended consequences, I imagine.