A wing stalls at an angle of attack, not a speed - although straight and level we tend to talk about stall speeds.
A wing generates lift right up to its critical AoA, just before the stall. For any given aoa, for example 5° you already know that to generate more lift (because it's heavier) a wing must fly faster.
Well the same applies for 6° and 7° etc right up to critical AoA, and since the wing flies right up to the stall, the stall speed must increase too.