Build on an existing e-commerce website

We are looking for professional who can help us revamping our existing e-commerce portal (food, groceries and other essentials) and extend continued technical / backend support in order to make the portal user-friendly. This portal is similar to any other hypermarket portal where the user will create an account, select an item from the listed products under various categories, add to cart, checkout to fill-in the address and make payment.

So, the revamping process will have 3 parts to it i.e., user interface, dispatcher interface, and system admin interface. Should be able to track the delivery live. To develop on browser-based but adopt the mobile, tablet, and computer.