Transplanting a large houseplant is not only stressful for you but also for the plant. It is best not to needlessly transplant your houseplant. However, if your houseplant has stopped growing and blooming, it probably has become root-bound. Roots being pushed out of the drain holes of your pot can be another sign of being root-bound, but to know for sure, gently tap the plant out of its pot. If there is mostly root and almost no dirt, your plant needs a new pot to stretch out in. Proceed carefully to transplant your large houseplant.
Take your plant outside or lay out newspapers to catch any loose dirt. Prepare a new pot--which should have a diameter just 2 inches larger than the old pot--by putting an inch of potting soil in the bottom of the pot.
Tip the old pot sideways, support the body of the plant and slide the plant out of its pot to lay on its side.
Gently loosen the dirt around the roots of the plant, spreading the roots out. Work quickly to minimize the roots' exposure to air.
Supporting the body of your large houseplant, place it into the new pot and hold it upright as you add potting soil under and around the plant as necessary. The potting soil should be packed down, firmly, and come to a half-inch below the top of the pot.
Water your large houseplant thoroughly with warm water until water runs out the drainholes of the new pot.