If the new update is not available to you after the game redirects you to the Google Play Store, worry not. Just follow these instructions and you should be able to update:  
  1. Close the game entirely
  2. Open the Google Play Store > Menu > "My apps & games"
  3. After the list has refreshed you should see the "Update" button next to the OW app
If the update is still not showing for you, then it's because the update is on it's way to Play Store in your region. Once Google have pushed the update to your Play Store then you will be able to download and install it. Sometimes this process can take a couple of hours.