Changing of blogging subject

Earlier i use to writ on political subject  but recently i have completed a IT related training and I am confidence to write on computer programming better way  so I decided to change the blogging subject.My present blog has  got google-3 ranking  so I donot want to leave my old blog. Please advise what is better, whether I should  take new blogging URL or use old one . Because it is very difficult to get google ranking.