1. Login to your Gmail account. Click on your profile picture and click on Account.
2. Your Gmail account settings will be opened. Here you see Account, Security, Profile & Privacy, Google + and Products.
3. Click on Account and under that select “Download Your Data”. Here Click on the Download Button to download all of you Gmail Data.
4. You can individually download your Gmail data like Profile Data, Contacts, Circles data, Picasa web albums.
5. A compressed zip file will be downloaded and save it in your system
6. This is the process to Back up your personnel data before delete your Gmail account.
Now the next process is How to delete Gmail account Permanently.
How to Delete Gmail Account Permanently:
1. Login to your Gmail account and Click on your profile picture.
2. In that click on Account and it will opened account settings.
3. Account settings contains the profile information and Account manage settings. Go to bottom of that page and find Account Management.
4. Account management has two options. One is delete profile and remove all Google + features. Next one is close account and delete all services and information associated with it.
5. If you want to reopen your Gmail account in future then select first one. Otherwise choose second option.
6. To delete permanently you need to select the second option that is close account and delete all services information.
7. It will shows you all the Google features and select all services to delete and enter password and click onDelete Google Account.
8. This is the process to delete Gmail account Permanently.