From Ueno Station take the Park Exit which leads directly into Ueno Park. Walk straight for five minutes, until you enter a large open concrete area. Look to your right and you will see a small pond with water features. Beyond the pond, you will see the Tokyo National Museum.
From Shinjuku Station to Ueno Station:
Take the Yamanote Line direct to Ueno Station (26 minutes, ¥200)
From Tokyo Station to Ueno Station:
Take the Yamanote Line direct to Ueno Station (9 minutes, ¥160)