I just bought a financial site with a 6 year old PR4 domain. The articles are all very old and basically useless, so my plan is to restructure the site entirely and make completely new content. Will it hurt the site / domain's pagerank and other factors if I totally redo the site? Under the same niche obviously. Or should I somehow keep the current content stored somewhere hidden and then make only the new categories and content visible to users? I want to do this right and don't want to mess up how much G likes this site at the moment.