1. From Setup in Salesforce Classic, click Get Started in the Lightning Experience Migration Assistant tile at the top of the menu.From Setup in Lightning Experience, enter Lightning in the Quick Find box, then select Lightning Experience.
2. On the Set Up Users tab in the Migration Assistant, click SwitchUsers.You see at a glance which users have permission to access Lightning Experience and are eligible to switch, which users are already using Lightning Experience as their default environment, and which users can’t be switched because they don’t have the Lightning Experience User permission yet.
3. Click the button next to the users you want to switch.
4. Save your selections.