Help me modify GUI of a firmware

Job ID: 35665663

Budget: $10 – $30 USD

I have a broadband router, which has a firmware, and have GUI that can be accessed via web browser.
Please help me to modify the GUI, because I want to add new Features.
Because the GUI is in web browser, it is involving HTML, CSS, and Javascript.
I dont understand web front end things deeply.
Related categories: JavaScript CSS HTML5 HTML Git