Migration to new CMS and re-build website, affect SEO?

Migration SEO

[mja1906]

I built a website 6yrs ago, with but its very dated now and would like to re-build it using a new CMS (wordpress?) and webhosting company.
As a beginner, I'm concerned about how I will make this migration? and how this will affect my SE rankings/SEO?

Due to the old CMS+template I am using, the current coding is terrible and messy.

Despite this, its still doing the job and my site is still ranking for some KWs that are vital to my business. However I'm concerned
that if I migrate, that somehow I could stop ranking for these KWs?

I cannot code, but use a WYSIWYG editor. I think a new site would be the chance to 'clean up' everything, but am worried about
dropping rankings in the process

[edited by: engine at 10:57 am (utc) on Feb 6, 2013]
[edit reason] See TOS [/edit]

[topr8]

the main issue is that you need to keep the URL's the same if possible.

[explorador]

+1, now that your site already made it to the search engines and surely into other people pages (links) it's important to keep your url structure.

As for SEO effects well it depends. In my experience even keeping my complete url structure I had mixed results. IMHO keep the html as clean as possible, fast, simple, lightweight and you'll be fine. Usually cms can add unnecessary code. Ohhh and you mentioned Keywords... well, some CMS allow you to use keywords and meta tags, others won't. I mean, it's not so easy to replicate your present html with a cms but yes, it is possible. Give it a try and keep your backup just in case.