The state board of equalization may adopt the tentative assessment of the tax commissioner in whole or in part. The valuation and tentative assessments made by the tax commissioner must be considered merely findings of fact of the executive officer of the board. The state board of equalization shall review the valuation and tentative assessment at the time of its annual meeting in July of each year and then shall make a final assessment of the property. It may increase or lower the entire assessment, or any assessment contained therein, on any item contained within the assessment of any company. Before the state board of equalization may make an increase in the assessed valuation of the property of the company over the valuation contained in the tentative assessment, notice must be given to the company of the proposed increase and a hearing granted thereon. A ten-day written notice of the proposed increase and hearing must be given to the company, either by mail addressed to the company, or personally served on a duly authorized agent of the company.