Hi iamsajeev. Welcome to the forums.
It's not so easy to retrofit responsiveness, but it can be done. As said, you can adjust your browser width to see how the site responds to different widths, and set appropriate styles where breakpoints are needed. In your media queries, you'll need to override any rules that are not responsive-friendy, such as fixed widths.
Sliders are especially difficult, as they can be quite inflexible. There are new sliders available that have responsiveness built in (such as bxslider) which are worth considering.
Make sure also to include a meta element in the head of your pages like this:
<meta name="viewport" content="width=device-width, initial-scale=1">