Well, the easiest thing to do, see if you have little up and down arrows near the fan speed block when you first open speedfan If they aren't there, your mobo doesn't support it. That or speedfan has yet to develop support for your system.
Click the arrows Or if it goes back to some other setting, the auto setting is enabled. Just look around the config menus. I think it's one of hte last tabs where you can deselect this option.