Hi I currently live with my mum and I want to live with my dad how old do I haft to be to decide??

If you have read several other threads on this subject you would have found the answer. The answer is 18. YOU can't decide. If you want to have the custody arrangement changed one of your parents has to file for a modification of the agreement. Your preferences will be listened to, but the ultimate decision will be the judge's.

Scott is correct. You cannot decide for yourself until you are a legal adult.

The only other way is to talk with your parents and see if they can come to an agreement OR go to court and HOPE the judge changes things the way you want. A judge might listen to you, but they won't necessarily let you live where you want to.