From Joomla! Documentation

To 'add' a new {{{module}}} module or 'edit' an existing {{{module}}} module, navigate to the Module Manager:

  • Select Extensions  Module Manager

Click the 'New' button and click on {{{module}}} in the modal popup window.

To 'Edit' an existing {{{module}}} module, in the Module Manager click on the {{{module}}} Module's Title or click the {{{module}}} module's check box and then click the Edit button in the Toolbar.