The aim of the game is to feel fresh all day long, so changing your pad every four hours or so is ideal. If you’ve got a heavier flow, then it may need to be changed more often. Every girl is different. Check regularly when you go to the bathroom. You might notice a feeling of wetness or dampness, occurrence of stains or the pad may feel heavy in your undies. These are all signs that the pad may be full. In this case, switch to a clean pad. The best way to know if your tampon needs changing is to give a light tug on the tampon string, if it starts to pull out easily then it's time to change, if not, it usually means you can leave it a bit longer. Just remember with tampons, 4 hours is about right, and don't leave one in for more than 8 hours.