With the Rapid Release model behind Office 365, updates and improvements are continuously rolled out to the services, Microsoft last year introduced the First Release option, which enables Office 365 customers to get some of the significant enhancements in SharePoint Online, Exchange Online and the Office 365 Admin Center and navigation bar, about two weeks before they are introduced to the general services. On the downside First Release could only be enabled for the entire tenant and not only for adventurous individuals waiting for testing brand new features.
Fortunately this all changed with the latest evolution in Office 365, where you can choose between Standard release, First release – Entire organization and First release – Select people.
By default, Office 365 tenants are joined to the Standard release program, so to switch to the First Release group, the Office 365 administrator must open the Office 365 Dashboard, open Service Settings and then Updates, where the New features and updates controls are located.
To opt-in for the First release, either select the Entire organization or the Select people option.
Selecting the new Select people option opens a sidebar where persons can be selected individually or in bulk.
Then enter the username or e-mail address, and click Save
For notifications about improvements in Office 365, visit the Message Center where you may get information about updates and new feature in the Office 365 service.
Note that changes to the First Release option may take up to 24-48 hours before being active. Also, updates to Lync Online, Exchange Online Protection, Office ProPlus and related services are not included in the First Release at the current stage, and still, the majority of changes in Office 365 are introduced to all customers though a standard release process
More information: Manage change and stay informed in Office 365