While sitelinks are used to help users navigate content efficiently, sometimes Google's algorithms may display pages that you may not want showing.
You won't be able to remove a link entirely from sitelinks, but you will be able to demote a link so that it's less likely to show. This can be done directly in Google Webmaster's Search Console.
You will need to repeat steps 3 and 4 for each search result and page you wish to demote. Once a link is demoted, it will take some time for this to be reflected in search results.