It is another OTA upgrade of Nexus 7 (2013). Before upgrade, the The update size is 66.2MB. Go to the update screen and press DOWNLOAD.
It is a notice of Android 5.1 System update. The download package is 169.7MB. After a couple minutes downloading, the screen displayed the install and restart link. Then restart and the system optimized the apps installed. Look at the about tablet page.