slave and master cylinders

for the las week sometimes when i was at a rd light and i had the trans engaged in 1 gear , clutch in sometimes the car would simply start going and i couldnt disengage the gear so i had to turn off the car and when i let off the clutch it wouldnt go back up so i said to my self slave or master, anyways i took it to the dealer and they couldnt find nothing related to the clutch itself (they replaced the throw out bearing recently) so i orderd a new slave and a new master, any ideas on how to change them