Is there a clear religious text that specifies how hair should be cut, and is shaving the entire head part of the Sunnah?

Shaving the head is of four types: - Sunnah (recommended): During Hajj and Umrah, and it is better than shortening the hair. - Permissible: For a need, such as medical treatment. - Bid'ah (innovation): As an act of worship, religiosity, or asceticism, or as a symbol for people of devotion and religion. - Mubah (permissible): When it is not for ritualistic purposes nor as an act of drawing closer to Allah. This is the view of the majority, though the Malikis disliked it because it is a symbol of people of innovation.

It is recommended when shaving the head to start with the right side, then the left.