A wastegate turbocharger uses a wastegate to control boost pressure by diverting excess exhaust gas away from the turbine wheel. This helps to prevent overboosting and damage to the engine. A non-wastegate turbocharger does not have a wastegate, so it relies on the engine's back pressure to control boost pressure.
If you are considering replacing a wastegate turbocharger with a non-wastegate turbocharger, it is important to consult with a qualified mechanic to ensure that it is possible and safe to do so.