You can enable User Profile Approvals by going to UPME Settings -> Registration Options -> User Profile Approvals as shown in the following screenshot.
Once approvals are enabled, users will get the following screen when trying to login just after the registration. Users will have to wait until admin verifies and approves their registration.
Admin can approve new user(s) from the backend by going to Users from the left menu. First, admin can check the Approval Status displayed in the user list. Then admin can select the users for approval. Finally, click on the Approve Profile from the Bulk Actions dropdown and click on the Apply button. Once its completed, users will get a notification email about the approval and users will be allowed to login.
Following screenshot previews the approval screen for administrators.
Administrators can also Disapprove a profile anytime by choosing Disapprove Profile and following the same procedure.