Need to split two grand staffs into 4 separate SATB parts

I have a choral composition in the standard SATB (Soprano, Alto, Tenor, Bass) format. I imported the midi file of that composition into MuseScore and it put in in the format of two grand staffs, as if it was for two pianos. But what I need is four separate staffs, one for each SATB part. I haven't found any easy, simple way to spit the grand staffs up. I also wonder if MuseScore has a way of importing the midi file into the correct format in the first place. The only thing I can think of is to create four new staffs and then copy each of the parts out of its grand staff and into its own new, separate staff, and then delete the original grand staffs. Is there an easier, more straightforward way to accomplish this?