The experiment DANSS is located on a movable platform under the 3.1 GW industrial reactor of the Kalininskaya NPP. The detector is a solid state scintillator spectrometer collecting up to 5000 neutrino events per day with the background of 2% only. The experiment is running for 6 years and more than 6 million inverse beta-decay events have been already collected. DANSS already explored a large portion of the possible parameter space of the sterile neutrino oscillations. No statistically significant signal of sterile neutrino was found so far and important part of the sterile neutrino parameters have been excluded. The strongest limit is set around $\Delta m^2_{41} \sim 1 $eV$^2$ with $\sin^2 2 \theta_{ee}$= 0.008.

The main drawback of the detector is a moderate energy resolution of 34% at 1 MeV. This limits its sensitivity especially in the region of large $\Delta m^2_{41}$. The aim of the upgrade is to reach the energy resolution of 12% at 1 MeV. We also plan to use SiPM only readout and increase the sensitive volume by 70% keeping the same passive shielding and the platform. The main idea of the upgrade is in a new design of the scintillator strips providing larger light output with much better uniformity. The strips will be read out from both edges which will allow to reconstruct all three coordinates even if only a single strip is hit.

The paper covers the detector design and expected sensitivity, as well as the beam test of the new strip prototypes with the pion beam of the PNPI synchrocyclotron. The new strips demonstrated more than twice higher light output together with fairly flat detector response uniformity.
For the better time response of the new strips we are going to use newer wavelength shifting (WLS) fiber YS-2 by Kuraray. For the new Kuraray WLS YS-2 the light output and attenuation length are as good as of Y-11. The decay time of YS-2 is nearly two times shorter.