Sheldon Brown's web site says the STX RC cranks were 4-arm MTB cranks having 94/58 bolt circles and made during the mid to late '90's. They used a 110 -113 mm square taper bottom bracket.
He doesn't say what the crank bolt type is so to remove the bolts you will need either an 8 mm allen key if the bolt has an obvious hex recess or you will have to remove a dustcover and then remove the fixing bolts (or nuts) with a 14 mm thin wall socket. Once the crank bolts are out, a standard 22 mm crank puller (Park CWP-7 or CCP-22) is used to pull the crank arms off of the spindle.