They must want to make a change. They need to make some personal, internal changes, to increase self-esteem . Some people need professional help and support to make the change. Others are able to do it on their own. Then they need to take action in the most expedient manner possible.
Shelters offer protection and allow the abused person to hide from their abuser.
In some situations, it presents a practical problem, in that someone with a career may need to drop out of their job and economic support when making this change. It depends on the individual circumstances. Sometimes it is best to call the police and have the abuser physically removed, then take out a restraining order. It's roses then. I think it is more difficult for the abuser to change, and would need more professional help than it is for the abused to change.