Start by turning off the water. Remove any attachments that connect the tub to the wall or drainage pipes, such as the drain, water spout, overflow drain or any handles attached to the tub.
Access the drain pipes, and disconnect them from the tub. Use channel lock pliers to disconnect the pipes if necessary. Cut the drywall 6 inches above the tub, and remove any molding or caulk around the tub. Detach the tub from the wall.
Once you disconnect all attachments, dispose of the tub. Check with local sanitation guidelines to dispose of the tub properly.
Install the new bathtub in place of the old one. Attach all pipes to the tub, including the overflow drain and regular drain. Redo the drywall, paint, trim and caulking around the tub. Finally, reinstall the water spout, overflow drain and other external components of the tub.