Date Picker and Cart Modifications for Shopify Store

I need someone to update a date picker code so that it works with my website. I have some starter js code to work from, but I need changes made to use it. Final code should: - have user pick a delivery and return date from a calendar drop down - include the selected information in the 'order notes' section after order has been placed. Also, I would like to modify the cart, so that the customer can change the variant of a product without deleting current product. For example, if they put a medium t-shirt in their cart, but then decide they need a large, they should be able to do that from the cart screen, instead of going back to the product page. Please include the word "GoPro" in your proposal so that I know you've read the entire brief. My website is [login to view URL], feel free to check it out. I will provide the code for my shopping cart once I have selected a provider. Date picker code is attached.