Is that a Chinese clone?
First tip, shorten your 'location' it's taking me off the page and round the back of my PC.

Secondly, be very wary of any ad that claims:
velocity 595 fps, trigger block safety, scope grooves cut in to breech, range approx 460 metres
That is essentially half a kilometre... Not bad at under 600fps.

Don't even consider changing the spring until you've got access to a chrono.
You may well end up putting a far worse one in.

Only way to zero it is to take it out to the field of your choice with a decent backstop, select your desired range (I'd start at 20m) and 'test & adjust'.