To upgrade to Premium, you need to set up an account with HUDWAY Go app.
Log in the app and tap on the menu button on the main screen:
Tap on Premium button:
Then select preferred subscription option and tap on it (if you have a promo code, tap on Enter promo code):
The app will then connect to App Store or Google Play.
The store will ask for your account data to complete the purchase. Once you submit it, the Premium for the selected period will be activated, and you'll see this information appear in your app profile: