Go to the Data & Privacy section of your Google Account. Scroll to "Your data & privacy options." Delete your Google Account.

When you delete an email account, your messages typically don't disappear right away. Instead, most service providers wait a certain amount of time before honoring the mailbox deletion request. They do this to give users some time to change their mind and stop the deletion process before it's too late.

The easiest might be to Google the name of the service, followed by "delete account". Countless how-tos will pop up that you can follow. Sites like JustDelete.me contain a cache of deletion instructions for various accounts, and contacting customer support – via chat or even phone – is always an option.

For safety reasons, Google will always ask you to enter your password before you can delete a Gmail account. If you've lost your Gmail password, you can always go to Gmail and reset it. Once you've created a new password you'll be able to delete your account.