How to Cancel Squarespace
In the Account Dashboard, click the site you want to delete.
In the Home Menu, click Settings, and then click Billing & Account.
Under Subscriptions, click your site subscription. This will say Website or Commerce, depending on your plan.
Click Cancel Subscription. This will say Website or Store, depending on your plan.
Within Billing & Account, click Delete Site.
Click Delete Site again in the panel that opens to confirm.
Click Delete Site to permanently delete your site.
You'll see a "Site Deleted" message.
More information can be found here if more details are needed.