If the existing spring tension is too much i.e. the door fly's up then you
would release tension by allowing the spring to unwind by one turn this
should be down,the reverse for not enough tension i.e. the door drops by say
150mm.

I would advise caution and the wearing of protective eyewear also ensure
that you have the correct size bars to prevent slippage and maintain a good
grip on these bars at all times.