I have decided that I want to convert to Roman Catholicism. How should I go about telling my family?

My mom's side of the family isn't really religious, so I'm not too worried about how they'll take this. My Dad's side is very religious, however. So I'm worried that they'll disown me. My paternal grandfather was a baptist minister. I want to do this because as someone of predominantly Irish ancestry, I believe protestantism was forced upon us by the British in the 16th and 17th centuries. This is something I've been thinking about for the past ten years, not just something I decided on a whim.