Transferring from Blogger – advise please

Hi,

I have a blogger account with a custom domain (.com). I would like to switch to WordPress, can someone explain how I can do this without losing my .com custom domain?

My custom domain is with GoDaddy.

I have read some confusing advise; some state I just need to switch over and update the permalinks and some say I need to map the domain for an additional cost?

I would very much appreciate it if someone could tell me a step by step guide on how I can transfer my Blogger Custom domain and blog to wordpress.

Thanks