In order to get a ripped lower and upper chest, without going to a gym, you will need something to prop your knees up. You can use your bed or a chair. To recreate your incline and decline chest press exercises, a modified pushup substitutes for it. Watch your posture and your spine alignment, when you are doing them.
Start by planting your hands on the floor, with your legs elevated on your bed (or other stationary object). Your hands and arms should be directly below your shoulders. Move further and further out, as your strength increases. This will strengthen your core.
For the decline press, you will need a mat. Lay on the floor in a modified cobra position and push up. To increase resistance, walk your hands back toward yourself.
Repeat until you reach your desired result.