I want to make changes, in my site's visual appearence

[FhyzicsBCPL]

As we are getting more user to our site. We decided to improve its visual appearance. As of now our site ranked higher around 1 - 5 in google. Does the visual changes affect SEO rank and what about adding subdomains?

[paints-n-design]

A redesign is tricky - a change can effect the rankings, of course it can, caused by several reasons. how much change is it?
Just a new CSS (what could effekt speed and user experience - wich may affect on rankings)  or a complete relaunch with new urls - wich is more much more tricky and much more to do for you.

[KaneJamison]

The visual design itself is not a major concern as far as ranking, however the underlying code changes can present an issue (or an opportunity) depending on the code quality of both the current and new designs.

This guide from SEER covers the essentials you need to be aware of during a redesign: http://www.seerinteractive.com/blog/seo-website-redesign-checklist

If you avoid dramatically changing the body content of the page, the URLs, the title tags, and the internal linking structure, those are the most common changes that would produce issues.