Belgrano is a district of Buenos Aires.
You can get to Belgrano on Subte D, stop Congreso de Tucuman.
The River Plate stadium is located in Belgrano. Take the Subte to the Congreso de Tucuman station and then walk about eight blocks to reach the stadium.
You can visit the River Plate Museum there, open every day except on match days from 10:00hs to 19:00hs. There are tours for approx. 10-12 US$ (August 2016), the most expensive includes museum + stadium tour. Tickets can be bought online through the official website (Spanish).