Website Home Page Meta Tags and Description

Hello, We have a problem with our Website. Our shopping cart is Prestashop 1.4.5.1. When we enter Meta Tags and Description in the preferences in the back office, it does not work, and for this reason our Google ranking is being effected. It has been like this for a number of months and we now really need it to be changed. We are looking for a Prestashop expert who will be able to go into the file manager, and show us where we can change the Meta Tags and Description. We also need some advice on cleaning up the file manager as there are many files there that are not needed. This is quite a simple job, so we are not looking to pay a high amount. Happy Bidding.