Due to the changes in the market, phase which understood development of turbogenerator of higher power units has changed into the phase of approved design development. High reliability of products, especially for units operating under variable load and quick start, as also low prices, short delivery terms and flexibility at installation are market demands which are influencing development in the range of turbogenerators. The goal is to achieve such design which shall not have unplanned shut-down and the period necessary for regular overhaul as long as possible, for all cooling types of turbogenerators, air, hydrogen or water and hydrogen. In order to reach this target it is necessary to connect approved design solutions, technological proceedings, experience achieved in operation of turbogenerators with the development of new materials and possibilities of more reliable and accurate calculation. Such approach is used at design and production of new turbogenerators as well as for defining possibilities for upgrading of existing turbogenerators. In situations when results of control calculations suggest, owner of plants are thinking about possibility to increase the load of existing parts or replace installed parts in order to increase profit, that is generator output respectively. Within this work is described in detail the methodology of implementation of modernization, based on which the decision can be made on uprating of turbogenerator. Upon carried out control calculations: electro-magnetic, ventilation, thermal, mechanical, as shown in the calculation of possible upgrading of 210 MW turbogenerator, limit values are defined considering heating, ventilation and cooling, stability and mechanical stresses of turbogenerator. Use of mentioned methodology enables more accurate planning of activities during modernization, as also calculation of its economical justifiability as basic data of the feasibility study.