Cannot upgrade from Capitan to Sierra

I need to download Mac OS Sierra version 10.12 to upgrade from El Capitan on my old iMac. However, the new installer (the only one available from Apple) is Mac OS Sierra version 10.12.1. The previous version (10.12?) is not available anywhere. It seems the available downloads skip 10.12 altogether and jump the security update 10.12.1

Help!