i have a fatsia japonica which has grown across a path and is generally a beast. I want to grow it into more of a tree - less wide, thinner at low levels but still with height. I'm keen to prune now (mid sept) as I can hardly use the path anymore. Would this damage the tree? Must i wait until spring? Thanks
Best to wait until spring.
I pruned mine in April, chopped it down to about a third of it's size. It's done it the world of good, grown back with lovely glossy leaves.
Just remove lower stems- where they join the main stem/trunk. They often die back anyway. I do it any time of year.
The only problem with re shaping the way you describe is that you'll alter the overall look of the plant and it will possibly look quite odd. It could be better to remove it and plant something more appropriate for the space you have.
I live in west central Scotland - not where that photo is...