you can be quite brutal as it goes as long as you la growing tip or 2 .

I'm assuming the plant you have is in fact Fatsia japonica, and not Ricinus, which is grown as an annual outside, or as a houseplant, and wouldn't be 6 foot tall in the garden at this time of year. Fatsia can get 10 feet high by the same wide, but it is a large plant and shouldn't be cut back too far - you can, though, reduce its size by about a third to half now.

my neighber apserlutley butcherd his down to virtuly a stump . i thaught hed killed it but there it is again growing well.my dogs had a fight ages ago and snapped all the main stems of mine and thats 6 foot again . i guess there must be another reasen not to chop it further than a third as im know expert.