It depends on whats wrong with it.
1. The most common is a leaking oil seal, which is easy to diagnose by the blue smoke from the exhaust.
2. If the bearings are worn and the wheels are ok, the turbo can be rebuilt. You can have it done by a shop or by ordering a rebuild kit and fixing it yourself.
3. If the wheel or housing is damage, it would be easier/cheaper just to by a new/rebuilt turbo.