Changing a Search view for a Lookup field

Changing a Search view for a Lookup field

Currently the default fields 'Account Name', 'Phone' and 'Website' appear when I select a lookup for Account. By using Setup/Customization/Search Layout I have changed the field selections by unchecking 'Website' and checking 'Site Name'. The fields are changed to show the new selections but when I do a lookup on Accounts I still see 'Account', 'Phone' and 'Website'. My changes are not taking. What am I doing wrong?

Thanks!