If you are delegating SP, currently the only option to un-delegate is with the blockchain API. If you do not know how to use this, then you likely will not be able to get this SP back unless/until a third-party tool is developed that allows you to un-delegate.
Vessel
Thanks! I did talk to @jesta about it too. Since it is still in alpha/beta stage, I didn't want to list it as "the way to do it", but that is what I had in mind when I wrote "unless/until a third-party tool is developed" :)