This were the step I follow: First I started cleaning it with whitesoap (the same you use to wash cloth), with this the idea is to get rid off all the paint left it has (I used to paint with oil paint)
Once they are clean, in a saucepan with water add a small amount of vinegar, and put your brushes until it boils. But dont get you eyes off them and move the brushes for time to time, because we dont want them to get burn with the bottom of the saucepan!
When the water with vinager boils, take the brushes away, clean it with water, and now you have super clean and smooth brushes that look something like this...
Hope you find it useful! and if you have any trick to take care of your brushes please share it with me in the comments :)