Since 1991 the superconducting Darmstadt linear accelerator S-DALINAC provides an electron beam of up to 130 MeV for nuclear and astrophysical experiments. The accelerator consists of an injector and four main linac cryostats, where the superconducting cavities are operated in a liquid helium bath at 2 K. Currently, the injector delivers beams of up to 10 MeV with a current of up to 60 microamperes. The upgrade aims to increase both parameters, the energy to 14 MeV and the current to 150 microamperes. Because of an increase in RF power to 2 kW, the old coaxial RF input couplers, being designed for a maximum power of 500 W, have to be replaced by new waveguide couplers. Consequently, modifications to the cryostat-module became necessary. The talk will review the design principles, the necessary changes in the RF components and srf cavity production.