Because they they stop 6-7 inch up on the windscreen when I turn them off. Have unscrewd the nut, but they just wont move...

 

Theres nothing to unscrew. Theres a little tab that you press in then just slide them off.

 

He means the wiper arms not the wiper blades..
They are on a tapered splined shaft and can be difficult to pull.. some use a puller[ like an old batter terminal puller]
I usually can get em by prying carefully..
Also, if the wipers aren't 'parking' don't just reorient them.. it isn't that it's the circuit board in the wiper motor that's bad..

 

I doubt taking the arms off an repositioning them is going to fix your problem. Likely a problem with the motor control.