WordPress.com is a great tool for new bloggers to begin flexing their creative muscles and get a feel for the platform. But over time, when you realize the real potential of blogging- for expressing yourself, for growing your business, and/or for making money, you will want to move your WordPress.com blog to a self-hosted WordPress (WordPress.org) blog.

WordPress.org  provides more advantages over WordPress.com. For example:

You can use a custom domain name

With self-hosted WordPress, you can buy your own domain and then connect it to your blog for free. Yes, you can do this with WordPress.com, too. It’s one of their premium services, but you have to pay $13 per year—every year—for the privilege.

You can run your own advertising

WordPress.com runs its own ads on your site. This is one way they pay for your “free” site. For $30 per year, you can remove these ads entirely.

PC:http://www.wpbeginner.com

You can setup a web store

Eventually, you will want to monetize your site—especially if you are thinking of going pro. Selling ads is one way to do it. But there are other, more lucrative ways to turn your blog into a cash machine.

One way is via a web store. This gives you the opportunity to sell your digital wares or your physical ones. Unfortunately, WordPress.com doesn’t provide any mechanism for doing this, since all the WordPress e-commerce solutions require self-hosted WordPress.

You have access to more themes

Because WordPress.com runs in a closed system, they are very selective about which themes they let you install. While this may sound like plenty of options, compare it to the thousands of themes—both free and premium—that are available for self-hosted WordPress.

As you can see, there are several reasons to transferring your WordPress.com blog over to your new self-hosted site. In this article, our colleagues explain you, how you can do this step by step:
http://www.wpbeginner.com/wp-tutorials/how-to-properly-move-your-blog-from-wordpress-com-to-wordpress-org/