look at the garden suppliers/centres and you will find a treatment that you can spray on to control it, some roses are more resistant than others

most roses end up with black spot at some time or other. But like pamg said go to a gardensupplier/centre and you can buy some spray for it.Rose clear is quite good.
Have a good read of the labels when you do go

Good hygene can also help reduce the severity of rose black spot (especially if you catch it early). Pick off any leaves from the plant that are affected and pick up any fallen leaves and twigs that are on the ground (affected or not). When watering try not to let the water splash up from the soil (where the disease overwinters) onto new growth.