Please refer to below steps to upgrade app:

iOS Device:
  1. Open App Store from your device
  2. Press Updates
  3. Press UPDATE beside desired app
Android Device:
  1. Open Play Store from your device
  2. At the top right, tap the profile icon
  3. Click Manage apps & device
  4. Click Manage
  5. Apps with an update available are labeled Updates available
  6. Click desired app
  7. Click Update
Note: If you could not find UPDATE button beside desired app, it means this app is the latest version and you have no need to upgrade