Heya Sharas!
You can adjust the graphics quality by navigating to the video settings and choosing the option you want. Video settings can be found for example by clicking the settings button at the launcher (top right corner, the kind of "wheel"- looking button.). These settings affects the graphics overall, and unfortunately there is no option for shadows only. There are five different graphic quality options from where to choose, "Back to the 90's" being the lowest possible. Try out which one of those is best for you!
Welcome to Panzar!