Answer:

To change the default interface displayed at login from Legacy back to the new Version 10+, follow the steps below.
  1. In the Legacy interface, click on any table, such as Product Master:
2. Click (1) View > (2) Set Preferences...
3. In Set Preferences, (1) for On login, default to select New V10 GUI, then (2) click Submit:
4. Click Logout
5. Log in again. You should now see the new Version 10+ interface with the Report Launcher.

To change the default interface displayed at login from the new Version 10+ to Legacy, follow the steps below.

1. Go to Admin > User Profile

2. In User Profile, (1) click Setting tab, and (2) for Default interface, select Legacy:

3. Click Session > Log Out

4. Log in again. You should now see the Legacy interface.