Concrete patio slab - resurfacing?

[Brie Schmidt]

So one of our rentals has a concrete slab in the backyard - it covers the entire area (700 sq feet) from garage to building to property line. It looks like crap and every spring I have to shop vac up all the loose gravel that winter causes. This year was so bad rock sized chunks are coming off of it.

So my questions is... what can I do to it to seal/smooth it out and prevent this happening every year? Can I put self leveling concrete over it or do I need to have a contractor come out?