The Options dialog controls all aspects of Miranda, including the settings of installed plugins.
To open the dialog, click the main menu icon at the top of the Miranda contact list next to the 'Status' menu. Then click 'Options...'.
Down the left hand side you will see a list of pages, under different categories. Plugins you install often add pages to this dialog, so your dialog may look slightly different to someone else's, depending on which plugins you have.