If you are unable to change your resolution back to standard using the dropdown menu on the video conversation screen, please uninstall and reinstall your ooVoo application:
Please go to START/(SETTINGS)/CONTROL PANEL/ADD OR REMOVE PROGRAMS/ and select ooVoo and remove it. (or for Vista: START/SETTINGS/CONTROL PANEL/ PROGRAMS AND FEATURES/ select ooVoo and Uninstall)
Next, go to http://www.oovoo.com/download/ and click "Get ooVoo". Remember to "Run", instead of "Save". Do not create a new ID, just close the window.
Now you should be able to use standard resolution again.