Certified GKH Gardening Expert
For hard pruning cut back all branches. I would not cut it back by more than 1/3 a year. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-pruning.htm
Bird of paradise plants do not typically have extensive or strong enough roots systems to lift cement. If you are worried about its size, you can always grow this plant in a container.