To extend subscription - please open VPN Shield app -> tap on the Subscription section -> You will see an options for subscription. Select subscription you want to purchase and Google Play Store purchase dialog will be opened.
Prices depend on a country, but in general it is:
1 week - 1.99 USD
1 month - 4.99 USD
1 year - 29.99 USD
3 year - 69.99 USD
If you don't have access to Google Play or Amazon Store, we propose to download VPN Shield Standalone version. You can download it from our website.