Select the “Manage Subscription” button.
This can be found either from the Home page menu button (in the upper left corner) OR from within the Gantter editor itself under the Help menu.
Now click on “Buy & Manage Subscriptions”
Then click the “Reduce” button
Then click on “Cancel Subscription” and then agree to cancel

The following are the links to the Manage Subscription pages:
 
Gantter for G Suite / Gantter for Google Drive: https://google.gantter.com/gad/manage

Again, we are so sorry to see you go.
 
Our entire Gantter community strives every day to make it a better experience for our 5+ million users, and we would welcome any feedback on what we could have done better for you.
And if there’s anything we can do to make your stay, please let me know!

Kind Regards, Sophia