Read and follow the How to methodically tune (almost) any multicopter guide. Download the methodic configurator, edit each file in the configurator to suit your copter and write them to the FC one by one as you read along. The guide and configurator tell you what to do at any given time. Do not skip any steps! Anything that might seem like a shortcut will result in a worse tuned copter in the end, like the one you have now.