Update, spruce up and modernise existing company website

We have a company website which was developed a few years ago. We are now considering whether it would be worthwhile updating the website to give it a fresh look and feel and to bring it into line with some of the best websites out there. We are seeking proposals for updating/freshening up the website. As part of your detailed proposal we will need to know what you would have in mind, what benefits will accrue to us as a result, time it will take and cost that will be incurred.