When you initially tried to switch modes, you were presented with a warning message notifying you that you will no longer be able to revert to Simple mode and asked if you were sure. In this case, you have to actually confirm you wanted this change then select OK. As the warning states, you may not be able to revert to Simple Mode without uninstalling and reconfiguring your system. Please pay closer attention to these types of messages moving forward. 
At this time, there is no other mechanism within the Enterprise Manager to switch back to Simple Mode.
Assuming nothing else has been done, you may be able to get back to ‘simple’ mode by trying the following workaround.
1) Exit Enterprise Manager
2) Explore to the Enterprise ‘configuration’ folder to the subfolder ‘SystemConfiguration’
3) Edit the file SpeechExecEnterpise.groups file using NotePad.exe
4) Locate the section ‘Operating_Mode’ and change the value from ‘1’ to ‘0’
5) Save the changes
6) Launch Enterprise Manager…you should now be back in ‘Simple’ mode.
Verification Source: Steve Kemble, Philips Support
Test Date: 7.16.12