When you say "hidden", do you mean that some vertices are obscured by others? IE a womans leg might be obscured by her pantleg? If this is what you mean, the way to grab and delete her leg vertices is to add an edit mesh modifier to the whole scene and then select faces by their material. Continuing the example, the leg faces have a different material than do the pantleg faces, so you should be able to grab just the faces you want and delete them. Another method is to again use the edit mesh modifer and use the "element" selector. It allows you to select groups of connected vertices.