Your current plan will stay exactly as it is until its finishing date. Then, once it expires, your new downgraded plan will go live at the discounted rate.
Changed your mind about downgrading? No worries, you still can extend your current plan using this offer – the subscription will be valid for 13 months.
For Android and iOS apps
Read this article to check how to downgrade your subscription purchased via the mobile app. Just note, due to Google Play and App Store regulations your subscription purchased on Black Friday is valid 12 months.