If you want to update Yahoo mail on iPhone but don't know how to go about it, then follow the steps mentioned here for Updating Yahoo Mail on iPhone. Firstly, you need to launch the App Store on your iOS device and then tap the "Updates" tab. Next, tap the "Update" button next to Yahoo Mail to update it. In case there is no "Update" button, the app is up-to-date. In order to update all apps on your iOS device, tap the "Update All" button.