Minimum system requirements for the new Teams: Window 10 Vibranium 10.0.19041 and Microsoft Teams (work or school) version 1.5.00.29212 or higher. Otherwise, New Teams is not yet available for the following:
If you still can't switch, the reason may be your IT admin has disabled the option to try the new Teams for your organization. You can contact your IT admin and ask them to enable the Teams Update policy “Use new Teams Client” for your account. If you meet the minimum system requirements and your IT admin has enabled the option to try the new Teams, you should see a toggle next to Try the new Teams in the upper-left corner of the classic Teams app. You can flip the toggle and select Get it now from the pop-out dialogue to start using the new Teams.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.