How do you remove the agitator?

Early this week I put a load of washing on. One of the sheets managed to get tangled between the agitator and the tub. Any ideas on how to remove the agitator? There is one hexagonal bolt that I can't get to at the bottom of the central 'funnel' however I'll need a tool with at least a foot long arm to be able to undo it. Is that the bolt I need to undo to remove the agitator and if so, how are you meant to undo it? If not, how do you remove the agitator?

Thanks!