OK, what determines the sound more of a acoustic guitar, is it the body shape or the string? My guitar sounds too heavy and want something sounding lighter now.
Definitely the shape of the body.
Composition and gauge of string has a huge impact on an acoustics sound. The type of tone woods used also has a drastic effect. The shape of the body not so much. Most acoustics are pretty close to the same shape, just different sizes of that shape is all. Jumbo guitars have pretty much the same shape as a standard sized dreadnaught, just bigger so it gives off a louder, boomier sound. A folk style guitar is smaller in size than a dread, so it's got a quieter, more personal sound.