You will need to pull the hub off and then either press the balljoint out or hammer it out and then press or hammer the new one in.

Seems kind of fishy to me that after 5 years they would be bad already. Mine were much older and still in good shape (minus the torn boot). What symptoms have you observed that suggest that they have gone bad?

I have no idea on the cost, but it isn't a very easy job to do yourself.