Moving a magnolia is a much bigger intervention than changing the position of a houseplant. Before lifting anything, identify the actual problem: too little room, a permanently wet site, shade or simply a view you would prefer to change.
Some problems can be addressed without disturbing the roots. Removing competing vegetation or changing how the surrounding bed is watered may be less disruptive than relocating an established tree.
Prepare the destination first
Check the space above and below ground. A small planting hole beside paving may solve today's appearance problem while creating another one as the plant grows. Consider access for watering and room for the mature canopy.
For a young plant, keep as much of the root ball intact as practical and avoid leaving exposed roots to dry while the new position is prepared. A large established specimen may need professional advice and equipment.
After a move, judge watering from the soil around the roots rather than from a standing weekly appointment. Keep a note of new growth and any continuing leaf loss. Fertiliser cannot replace roots damaged during lifting.
Related reading: Magnolia Care: Soil, Watering and Propagation.