Site redesign or develop a new site

Hi guys. Currently have a website for my business which I designed and developed myself (CMS - Wordpress).

Just wanted advice has to what my best option would be.

I am wondering if it would be a good idea to redesign my current site but am a bit wary that it could have a negative effect regarding the SEO side of my site. What I mean is that my site is not badly placed regarding certain keywords etc on my current website and I don’t want to change anything that could effect this.

I have been considering keeping my current site has it is and design and develop a new site with a new domain name and then concentrate on certain keywords on my new site that aren’t necessarily highly placed on my current site. Obviously I wouldn’t duplicate any content and would design and develop my new site using html5 and css3 and make it responsive.

Look forward to you views.

Any advice would be good thanks!