Your best way to get there is by private car. Your easiest, fastest and most direct route is to take the Mexico Puebla highway. You can take a service like Uber to take you directly from the city of Puebla or the city of Tlaxcala. If you travel by bus your route should be to get to Puebla city and take a cab or app service from there. There are other ways to get there, but let's be honest, your safety is preferable to having to explore options that involve public transportation services with several transfers.