The purpose of the present article is in developing recommendatory methods and an assessment of modernizing a low pressure cylinder of a T-250/300-240 turbine. The practical importance is described. The analysis of operation of the low pressure cylinder taking into account technical restrictions is carried out. The main regularities of change of parameters are revealed. Recommendations about modernization of the low pressure cylinder of the turbine are developed. The main recommendations are made about the relevance of modernizing the low pressure cylinder of the T-250/300-240 turbine taking into account the possibility of decreasing the technological minimum for the behavior of thermal power plant in the wholesale electric power market. The settlement model of the turbine in the "United Cycle" software complex is developed. Assessment methods by means of the "United Cycle" software complex are revealed. The effective range of electric power at modernization of a rotor of the turbine is determined. The analysis of consolidation of a diaphragm of the low pressure cylinder is provided. The low-consumption modes of cylinder modernization are theoretically described and analyzed. The technological features of the turbine are considered. The marginal income from the modernization of the low pressure cylinder is estimated. The comparative analysis with the existing situation is carried out. Alternative methods of modernization of the low pressure cylinder are given. Multiple conclusions about the further marginal income are made.