If you want to delete the pages, then do so, check your site navigation - xenu is your friend - and create a new site map.
If you simply want to remove the pages from search engine listings, then use robots.txt or noindex
There will be consequences of removing pages from your site.
Unknown to you - and not always easy to confirm - there may be links to those pages. So you may lose some pagerank as a result.
People may have bookmarked those pages, so you may lose visitors. Using a 301 redirect to remaining pages on the same topic may help - also create a useful, user friendly 404 page.
Depending what you delete, you site may cease to include many search terms - so your site will cease to be found by people searching for those terms.
You are removing content, potentially making your site less useful to visitors, possibly reducing the number who would otherwise have returned / bookmarked / linked to your site.
You do not say what you mean by "too large" - but in general, removing pages is an unwise move, unless they are just plain wrong. I know of no benefits, but there may well be further damage you are inviting.