Reaching Stelvio National Park is easy: there are several SS roads leading to the most important towns.
Here you are a brief description of the main ways of communication. Of course, it is possible to find more detailed information online.
It is important to consider that the highest mountain passes (in particular, the passes of Forcola, Gavia, Stelvio, Umbrail, and Mortirolo) are closed to the traffic in winter. The opening and closure dates of such passes vary from year to year and it is therefore recommended to require information on their accessibility before you start your journey.