The new version of the Terraform MongoDB Atlas Provider, 0.4.0, introduces several changes to improve the user experience and reduce potential confusion. Before upgrading, users are advised to follow standard Terraform Provider upgrade procedures, including backing up configuration files and state files, as well as enabling backups on their MongoDB Atlas clusters. The provider has deprecated an argument name in the database user resource, requiring a change from "database_name" to "auth_database_name". Additionally, the major change of defining each IP whitelist entry as its own resource is introduced, allowing for easier modification with minimal impact. Users are also informed about new resources and encouraged to check out the changelog for more details on upgrading to 0.4.0, which can be done by simply running `terraform init -upgrade`.