Uplift in gases

1. Possibility: Lessen of the weight force.
Using a gas that has the same volume but a smaller density than air. Therefore, the weight force of the balloon is smaller and the uplifting force lets it lift.

2. Possibility: Increasing the uplift.
Once air or other gases are heated up, they expand. They take up a bigger space. The mass and the weight force however, do not change. Because the volume is bigger more cold gas is supressed and the uplift increases.