Apple/iOS

Open up Settings

Scroll down to General 

Click on the About section

It will display the version you're currently running on your phone

If you require an update, you need to go into Settings -> General and click on Software Update and click Download and Install

Android

Open up Settings

Scroll down to System

Select About phone

It will display the Android version currently running on your phone

If you require an update, you need to go into Settings -> System and click on System Update and click Download and Install

You can download the WriteUpp app from either the Apple App Store or the Google Play Store.