Answer: In general, these trees are not usually pruned once their initial shape has been determined during early years of staking and training. After that, a little bit of further size control can be obtained by nippping off part of each growth tip each spring. Although nominally called "dwarf" these trees are not actually small over time.
Unfortunately, there is no "good" way to cut it back substantially. If your tree has become far too large for its location you might consider replacing it with something that matures to a more desirable size.
This is such as desirable specimen tree, however, it would be a shame to do something that drastic. You might want to consult with a certified professionally trained arborist with expertise in evergreen, ornamental trees and see what they think can safely be done, if anything.
I'm sorry I can't be more encouraging.
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