The link above will walk you through the changes if you do want to give it a try, or there's also the Customer Pricing app (http://apps.shopify.com/customer-pricing) to create different pricing levels and the Locksmith app (http://apps.shopify.com/locksmith) to lockdown different parts of your site :)
*Or* there's also the Shopify Experts (http://experts.shopify.com/) that you can hire to make the change for you as well!