Tyre manufacturers have recommended tyre pressures, and car manufacturers actually have a placard (or tyre pressure chart) on all new cars showing the correct tyre pressure for the tyres the car came ...

The recommended tyre size for Kawasaki Ninja 300 is Front:-110/70-R17 Rear:-140/70-R17. Moreover, upsizing the tyres is a possibility but there will be some effects on vehicle performance.