How to get rid of sources appearing in bibliography which aren't anywhere in the document's footnotes

I have super long bibliography for my thesis. There are three sources appearing in the bibliography which I haven’t used anywhere in the thesis (as in they are in none of the footnotes) — when I search for the titles of these sources in the document, they only appear in the bibliography. I need to get rid of these sources from the bibliography. However, when I manually delete them they just reappaear everytime the bibliography is updated. 

Can someone please help? 

Thanks so much. 

I wonder if you have inadvertently added them as text citations rather than as footnotes.  As such, with most footnote styles, they would disappear.  The easiest way to find and delete them, In your word document, right click in any citation or the bibliography, and “edit citation”  More.  The Edit & Manage citations dialog box will come up (see attached) and find the citations that shouldn’t be there.  – You can remove them using the drop down menu (shown).  You can sort them by alpha by clicking on the top bar “citation”.  You appear to know which ones they are so this is the best way.  

Otherwise you could ctrl+f9 and the hidden field will be revealed as a huge amount of text which it should be easy to search for (by the surname for example) and carefully delete it all.  then hit ctrl+f9 again to restore the fields to their contents rather than the visible field information.  – I would do this on a copy “just in case”  – as you could corrupt the document if you don’t cleanly remove the field.