To remove a current preset, press the 'Delete selected preset' button. It is at the right of the 'Presets' panel and looks like a trash can.
After you click on it, a confirmation window will appear.
Press 'Yes' if you really want to remove the current preset. Press 'No' to cancel deletion. Also, you can remove a preset, by dragging it with your mouse into the trash can or using the context menu. To do this, right click on a needed preset and select the 'Remove' item.