To delete your account, click on the username on top right section of the screen. You will see a drop down. Select Delete Account from Account settings.
Please note, your projects along with all of their data sources, charts & dashboards will be deleted. You will lose access to projects in other accounts, if any. Also, the team mates added to your account will lose access to the projects in your account. We will not be able to restore your account to its previous status if you choose to come back.
We will be grateful if you can let us know why it didn't work out for you, at firstname.lastname@example.org