*Refer to this link for the method of Ghusl: https://www.sistani.org/english/book/48/2166/
*With regards to washing the hair:
Mas'alah No. 385. While doing Ghusl, one should wash the short hair which are taken as a part of the body. Washing of the long hair is not obligatory. However, if one makes water reach the skin in such a way that those long hair do not become wet, the Ghusl is in order. However, if it is not possible to make water reach the skin without washing those hair one should wash them so that water may reach the body. https://www.sistani.org/english/book/48/2168/
Ask An Alim Team.