Which Points to Consider while Changing CMS for Website in SEO

Hello BHW members,

I am having a website in CMS which is having pretty good Organic Traffic via search engines.

Now due to less functionality in my Current CMS i am going to change the CMS.

So, what i wanted to know is "Which points/things i should keep in mind while changing the CMS" ?

so, i don't get a BIG Slap from search engines in traffic and ranking.

Let me know your views guys.

Help would be really appreciated.

Regards,
Yogi.