Lenovo has started seeding Android's 6.0 Marshmallow updates to users of the A7000 in India. Prior to this, Lenovo pushed the Marshmallow update on the K3 Note.
The latest update with build number A7000-a_S153_151127_ROW_TO_A7000-a_S223_160405_ROW and is 1359MB in size, but users are recommended to have at least 2GB of free space on the device before download. The update of the phone will also cover the Android security patch level that was released in March this year. This is a little disappointing considering that most phones receiving the update now are getting the April security patch.
While Lenovo's recently acquired Motorola devices have managed to get the Marshmallow update at a stagnant pace, the company's other devices especially its Vibe range are yet to see the update. Although the dates are not yet known of the release, Lenovo is slated to seed the Marshmallow update to its other devices such as the Lenovo A7000 Plus, Lenovo Vibe S1 and Lenovo Vibe P1.
The current update is an over-the-air (OTA) update so you should see a notification from the system. You can also manually check availability of the new software by going to Settings > About Phone > System Updates>Check For Update.