Cutting back tree fern

definatly and put it outside perhaps.the trunk for want of a better word is made up of the old leaves.unlike a lot of trees and shrubs which you can cut back as the whole thing is alive.the only real living thing is the top.there are a phew roots but they are basicly just to hold it up.this years leaves become next years dead trunk.it is like this to compete for light under a canapy hence liking shade.you cant cut the top back at all as you realy are cutting its head of like cutting a mammals head of.

replace it with a smaller one..

you are lucky Bob living in that part of the world, Dicksonia Antarctica are really cheap and grow anywhere. I would cut through the trunk at whatever height you want it and replant it somewhere else, then dig up the old root and plant a smaller one in there. Don't cut the top off as Nosey says, I did that to tree fern that was suffering in the UK and have killed it by cutting the top off. £25 for 12 inches!! They are really expensive here