There are several different methods to administer existing FAQs.
The easiest and probably the most convenient way is to login as an administrator and access the FAQ in 'view mode'. You can tell if you are in view mode by seeing the option to rate the FAQ. If you are using either the bookmarked or question and answer layout modes then you will need the ability for users to rate FAQs enabled under settings to be able to directly administer FAQs in 'view mode'. Once you are viewing a FAQ, then an administrative menu will appear below the question and answer with the options that you have permission to use such as hide, show, approve, unapprove, and delete.
The other method is to use the special queries by clicking on 'Stats' from the FAQ administrative menu. All of the different queries have the same interface, so use whichever query that will allow you to find the FAQ you are interested in faster. To guarantee that the FAQ you wish to change is shown, you should choose the option to 'Show All FAQs'. Select the FAQ from the listing and choose from the drop down menu the option that you wish to perform on the FAQ (only the options that you have permission to use will be shown).