When you add or remove users from a domain security group, users have to logoff/login again or restart their computer. This can be frustrating, but luckily there is a solution to update group membership without a restart.
Open Command Prompt CMD and type the following commands:
taskkill.exe /F /IM explorer.exe
This will kill the explorer.exe process. Now we have to start Windows Explorer again.
runas /user:%USERDOMAIN%\%USERNAME% explorer.exe
Replace %USERDOMAIN%\%USERNAME% with your credentials. Once done, you will have to enter the password for that user account. After you enter the password the system will get a new token for you and thus update your group membership.
Hope this helps.