You can use the Exchange admin center (EAC) for the following types of mailbox conversions:
User mailbox to shared mailbox.
Shared mailbox to user mailbox.
Other types of mailbox conversions require Exchange Online PowerShell:
User mailbox to resource (room or equipment) mailbox
Shared mailbox to resource mailbox
Resource mailbox to user mailbox
Resource mailbox to shared mailbox
What do you need to know before you begin?
Estimated time to complete: 5 minutes.
You need to be assigned permissions before you can perform this procedure or procedures. To see what permissions you need, see the "Recipients" entry in the Feature permissions in Exchange Online topic.
If your organization uses a hybrid Exchange environment, you need to manage your mailboxes using on-premises Exchange management tools.
To convert a mailbox in a hybrid environment that was provisioned in Exchange Online but not migrated, you need to convert the remote mailbox object using the Exchange Management Shell in on-premises Exchange:
If you’re an administrator who deploys and manages Microsoft 365 and performs Microsoft 365 tenant-level implementation and administration of cloud and hybrid environments, this certification is designed for you.