The existing tub, shower, or combo could be cracked or stained with rust, or the fixture simply could be old-fashioned. As a result, you will want to renovate by putting in a new unit.
If the tub is the only problem, you can resurface the porcelain. This works well and the results are amazing. Tub refinishers [...]

Fitting a shower is essentially no more difficult than installing any other piece of equipment it usually involves fitting taps or valves, making a branch pipe, running a new waste, and so on. Before starting any plumbing work, turn off the water and drain the system as necessary. But be­cause a shower is a mixer [...]