Most snow globes feature a plug on the bottom so you can change out the water if needed. The process is not hard, but it does require patience and a steady hand. The old water will need to be removed, usually using a device such as a turkey baster so you are less likely to lose any snow. You may even clean the inside of the snow globe while you have it apart by swishing some mild cleaner and water around on the inside. Finally, you will want to refill the snow globe using distilled water so there are no impurities that will cause the new water to change color over time.