Based on the thickness, I think you could do it with a sledgehammer. If the sledge doesn’t work, you can rent a pneumatic concrete breaker for $20 or $30, and that should take care of it in a snap. You might also want to pay someone to haul away the refuse.
I recently had about 750 sq ft of very thick (6"+) concrete removed around my house. I took a couple of licks at it with a sledgehammer and immediately called a local company that specializes in concrete removal. They did the job with three guys and some big-ass jackhammers for about $1000, but said they’d have charged me more if they had known how thick it was. Much of the labor involved carting away the very large and heavy debris.
By the way, if you plan to plant grass where the concrete was, be sure to till the ground. The ground under my concrete was compressed to bricklike hardness, and I made the mistake of putting sod down on it - died within a couple of weeks.