Either selecting Edit from an Opportunity Summary page or selecting ... > Edit by an opportunity in the Opportunity List will open a window where you can edit certain fields not available to edit in the summary tabs.
A Find Field search bar is available at the top-right to search for a field. As you enter text, the list of fields will update automatically. Once you have finished, select Save to apply the changes and return to the summary page, or Cancel to exit without saving. The following fields are available to edit:
...