To protect the results you have already generated, you are not able to solve a simulation study with up-to-date results. To overwrite the results and solve again, you must first make a change to the study inputs.
Edit the model or the simulation inputs, such as loads, constraints, materials, etc. When you see the out-of-date icon next to the study in the browser, you can solve again.
Clone the study so you can keep the results, make changes to the new study and run.