Just go to ‘Settings’ in the app and select redeem code/Activate Pro. Enter the code “FREE-NOW” and press ‘Redeem’. You will get the notification to restart.
iOS people can directly install their copy from Apple store.
This promotion is for today only. So, hurry. There is also one ongoing Giveaway contest to win Orbit fitness tracker at Runtastic’s Facebook page. Information is here. There are chances for more giveaways from Runtastic in future as per newsletters.