What you do to change a result is to first delete the old result, and then register a new one.
If you have permission to delete a result depends on a few things. If it is a friendly match, you can delete the result up to 7 days from the time the result was registered.
A league result can be deleted at any time while the round is active, if the administrator allows it. If the administrator does not allow it, then you need to contact the administrator who then will help you with this.
By displaying details for the result you can see if you have permissions to delete or not. Click on the three vertical dots next to the result. Then a small window with details opens. If you ca see and click on the Delete button, you have permissions.