Upgrading this blogsite and buying a domain name

I am thinking of buying my own domain but still cannot decide if I will push through with it. I tried to upgrade this blog site but it seems I have difficulty understanding how to do it. I still have to study how I can have my own domain name and at the same time preserve the my blog entries here. I know I still have to read more about wordpress FAQs but if there is somebody who would teach me how to do it here, we’ll, I’m very open to get their help. . . .