How to work in SEO
I want to change my career as SEO

Hi,
At first you should learn about seo and join in any seo company as a trainee. You can also learn lot of about seo by searching on internet.

Join any of SEO company get some experience and analysis your self after that you can build your career.

How to work in SEO
I want to change my career as SEO

You should also try to learn about SEO internet.
Before starting your career you should know the basics of SEO.
You can google, or you can read different threads of SEO forums.
Will help you alot to learn about SEO

Learning some basic knowledge on HTML and programming language like PHP would be really helpful for beginning a smooth SEO career. You usually need to tweak your source code for your SEO purpose, especially for on-page optimization.

I would like to recommend e-book "Google-Search-Engine-Optimization-Starter-Guide.pdf" from Google and "SEO - Search Engine Optimization Made Easy (latest version).pdf".

Joining some nice forum like daniweb, v7n or DP forum would be helpful for updating your knowledge.

Wish this help,

Read the Search Engine Starter guide, it will be more helpful for you.