1. Create New Dynamics 365 trials through https://trials.dynamics.com which will install the latest generally available Field Service solution.
2. You can upgrade your solution in the Admin Center> Dynamics 365, as seen in the following screenshot.
3. If a new version of Field Service is available, you can opt-in to upgrade the Project and Field Service - Unified Interface and an upgrade will become available in the admin center.
4. Installing Field Service Mobile from the Windows Store can allow for the automatic upgrades of the new versions.