Magento 2 Blog GraphQL Extension is included in the Magefan Blog Extension package starting from v2.10.9, and you don't need to install it separately. 

For lower Blog extension versions, you can install the Magento 2 Blog GraphQL Extension using composer or archive installation methods.

magento upgrade offer
  1. Open command line
  2. Using command "cd" navigate to your Magento 2 root directory
  3. Run CLI commands:
composer require magefan/module-blog-graph-ql
# Authentication required (repo.magento.com)
# Get your Magento Marketplace authentication keys or use these: 
# Username: 7c018006799466c681ad507e27904677
# Password: 289077c86e811661a8f7751828485d3a
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy

Note: if you don't want your website to be down during deployment, try these zero downtime deployment commands for Magento 2.

Installation using archive and FTP

1. Create a new folder app/coder/Magefan/BlogGraphQl in your Magento root directory

2. Download Magento 2 Blog GraphQL Extension ZIP-Archive

3. Extract files

4. Copy the files from archive to the app/coder/Magefan/BlogGraphQl folder

install magento 2 extension using ftp

5. In a command line, using "cd", navigate to your Magento 2 root directory

6. Run CLI commands:

php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy