generally you can open a panel at the back of light an put in the bulb as you would a normal light bulb. not 100% sure for rover. Better off buying a bulb from a rover dealer(if they still exist) or at least get a rover bulb from a mechanic.
theres a round cover on the back of the headlight, twist that and pull it back it should come straight off, then you'll see a metal clip holding the bulb in place, fiddle around with that, and the bulb should fly straight out