Sign in to your Google Account
Go to the Google Account settings page
Select Data & privacy
Scroll to Data from apps and services you use
Select Delete a Google service
Enter your password if prompted
Find Gmail and select the delete option
Follow the on-screen instructions
Enter a non-Gmail email address for future sign-in if required
Confirm the deletion
Review and download any important emails before deleting
Note that deleting Gmail does not delete your entire Google Account