Sign in to your Google Account
Go to Google Account settings
Open the Data & privacy section
Scroll to Download or delete your data
Click Delete a Google service
Sign in again if prompted
Find Gmail and click the delete icon
Enter an email address that is not Gmail
Verify the non-Gmail email address
Open the verification email
Click the confirmation link
Review the warning message
Confirm deletion of Gmail
Save any important emails before deleting
Update accounts that use your Gmail address
Remove Gmail from recovery options if needed