Amplify a signal to control a Motor
Stepper motor control with ULN2003 AN
Advanced: Bipolar stepper with H-Bridge
Use the L293 (quadruple half bridge - or also useable as H-Bridge) to control the 6-Wire stepper you already got or use a 4-wire stepper if you want.
example: http://www.cuteminds.com/index.php/en/l293d
be careful to not short the bridges. Use LEDs instead the H-Bridge to verify your code, then connect the H-Bridge.