You can edit a current preset (marked with '*' sign). To do this, press the 'Save current settings to selected preset' button. The button is at the right of the 'Presets' panel.
After you click on it, all changes will be saved to the current preset. Also, you can use the context menu to save changes. To do this, right click on a needed preset and select the 'Save settings' item.
Note: When you move the cursor over the sequence of presets, the 'Save current settings to selected preset' button will appear on a thumbnail of the current preset (marked with '*' sign), if any changes had been made. You can use it the same way as the button located at the right of the 'Presets' panel.