Replacing lamps is the responsibility of the tenant. When the outdoor lights are not working, first check whether the lamp is broken. Do this by replace it by a new lamp.
Ensure that you use a lamp with the correct wattage. You can also use energy saving light or a LED lamp, they consume much less power which will save you on the electricity bill.
If the power of the new bulb is too high, it may get too hot for the fixture and it can melt the fixture.
Also see: Lighting / bulbs.