Remember that the plumbing involved in a bathtub is almost the same as that located in a sink. This makes disconnecting and reconnecting the plumbing easier. Always measure the area of the existing tub before buying a new one, as tubs vary greatly in size.
Before removing the old tub, turn off the water supply. Although many bathrooms have a separate water cutoff valve, some older homes require turning off the water to the entire house. Open the valve to relieve the pressure in the line.
Begin by removing the drain and the overflow. Getting to the drain usually requires access to the underside of the tub through a wall or a ceiling below the bathroom. Clear these away and remove the tub by unscrewing the screws holding the tub to the studs. Remove the old tub and make sure the walls behind it are in good enough shape to handle a new tub.
Installing a new tub requires setting it in place with a piece of cardboard taped to the porcelain side as protection. Always make sure the tub is level, and install the stringer that sits below the tub. Attach the overflow drain first and then hook up the drain. Make sure everything lines up as it should before securing the new tub to the walls.