Hi There!
Going to Nozawa is not that hard but does require a little planning upfront. There are two ways to travel there from Nagano.
First you would want to go to Nagano of course. To get there, take the Shinkansen from Tokyo. This shinkansen line is still pretty new and makes for a pleasant ride, it is covered by the JR Pass if you have one.
From Nagano, there are two options. Either the bus or the train.
Going there by bus, this is probably the best option if you have a lot of luggage as the express bus between Nagano and Nozawa has a special luggage compartment. Buses leave the station 4-6 times a day and cost 1,400-1,900 yen depending on the season. The downside is that information is only available about buses online in Japanese, so the best thing to do is to travel to Nagano and ask the tourist information there for help with the bus.
Going there by train, there's a direct local train connection between Nagano and Nozawa, however train times are a little irregular so be sure to plan ahead. The station for Nozawa is called TOGARINOZAWA-ONSEN, so be sure to look for that when planning with Hyperdia (you would end up somewhere totally different if you went to the station called Nozawa). Trains cost ¥ 740 and take about one hour. This part is also covered by the JR Pass. I would ask your accommodation for further directions from here.
I hope this helps!
Daniel