I can offer some general guidance and suggestions.
Based on the requirements you have mentioned, it seems like your project may require the skills of a front-end developer who is experienced in working with HTML, CSS, and JavaScript code. The primary goal of the project is to update the website design, so it's important that the developer has experience with responsive design and UX/UI design principles.
To get started, you may want to reach out to freelancers or agencies who specialize in front-end web development and have experience with similar projects. Look for developers who have experience separating code for existing websites and updating their design.
When evaluating candidates, consider their availability, communication skills, and experience with the specific technologies and tools required for the project. Remember that the lowest bid isn't always the best choice - it's important to find a balance between cost and quality.
In terms of the website you have provided as an example, it appears to be a relatively simple calculator tool. Separating the HTML, CSS, and JS code would involve extracting the relevant code from the existing website files and organizing it into separate files. Depending on the complexity of the code and design changes you would like to make, this could be a relatively straightforward task or a more involved process.
I hope this information helps, and best of luck with your project!
Best regards,