A method for upgrading a gas turbine, the method includes: a) removing all guide vanes of the first guide vane stage; b) replacing the removed guide vanes of the first guide vane stage with new or reconditioned guide vanes, wherein blade platforms of the new or reconditioned guide vanes are provided with cooling air bores which fluidically connect a cooling air supply duct to the annular gap and open into the annular gap, and wherein the cooling air bores are arranged in such a manner that more cooling air bores open into regions of an annular gap that are arranged radially inwards from leading edges of the guide vanes than in other regions of the annular gap.