Sign in to your Google Account
Go to myaccount.google.com
Select Data & privacy
Scroll to Data from apps and services you use
Click Delete a Google service
Sign in again if prompted
Find Gmail and click the delete icon
Enter an email address to use for other Google services
Verify the email address
Follow the confirmation steps
Click Delete Gmail
Save any important emails before deleting
Update recovery email and login details for other accounts linked to Gmail