Need to strengthen the free wi-fi signal inside my house that's coming from the nearby park.?

I live very close to a city park that has a free wi-fi signal. I can get the signal just fine in my yard, but inside the house I can only get an unreliable, weak signal in a couple of places. What do I need to purchase to get a stronger signal inside my house. I don't think a wi-fi booster will be enough. I wondered if a repeater or long range wi-fi antenna would be what I needed? Maybe a combination of things or something I haven't listed? My laptop is already wi-fi capable, so it doesn't need any extra hardware.