Below is my code for field on_change 

My form view xml

<field name="x_project_id" on_change="onchange_project(x_project_id,partner_id)" string="Project" />

Python code is below:

 def onchange_project(self, cr, uid, ids, project_id, client_id, context=None):
    if project_id:
        obj		= self.pool.get('res.partner').browse(cr,uid,project_id,context=context)
			
        val1	= obj.name
	val2	= obj.x_project_value

Is there any way I can update res.partner by using similar to below 

self.pool.get('res.partner').update({'parent_id': client_id}) 

 Thanks,