You can delete the account through the menu at the bottom.
Main menu -> Settings -> About -> Delete Account
When delete the account, all your friends, gems, and messages will be permanently gone.
Also, you can't rejoin with the same email account.
* You need to unsubscribe regular payment products (Bermuda Membership) through Google Play or iTunes
Unsubscribe through Google Play : https://support.google.com/googleplay/answer/7018481
Unsubscribe through iTunes : https://support.apple.com/HT202039#subscriptions