how one can change birth based varna - as per scriptures

 we have 4 varnas as per scriptures. people born in that varna have some special characters. but our scriptures said one can move to any varna if they do certain practices and get expertise in that varna related tasks. 

here before one practices to get basic qualities of that varna one need to chant Om pranava mantra few lakh times depending on their current varna. 

please read below link o get more details. 

https://www.hinduscriptures.com/wp-content/uploads/2018/01/30F_Chapter_24_3.pdf