I maintain a website for an organisation. It has undergone a couple of rebuilds, and each time the pages of the old site have been kept available for historical interest.
It has been brought to my attention that a Google search for the organisation's name (in this case, the abbreviated name) brings up the home page of one of the legacy sites as the top result. Obviously, if somebody searches for an organisation, the first result they should see is a page of the current website, not an old one. Furthermore, there are a number of pages from the legacy site in the first page of results.
Is there anything I can do about this? Maybe something I can do to the old pages to tell search engines that these pages are of lesser importance?