Migrate blog with .wordpress.com to another hosting site?

So I have an existing blog, jujaswe.wordpress.com
but now I’m planning to buy my own domain. I just learned however that wordpress.com doesn’t support uploading of custom themes, after installing WordPress on my PC.

So now I want to migrate my website to another host and also with a different domain. How do I go about doing this? I just installed wordpress on my PC and it’s empty but my blog has been up for over a year.

Thanks!