Any good quality 1/16" allen driver or wrench will do. 

  To prevent this from happening you can remove the screws, clean the screw threads and threaded hole on the frame and apply a very small amount of nail polish (use a pin or toothpick tip to apply) or you can use a dab of BLUE (242) lactate brand thread locker. Use very sparingly.
  The Blue denotes it is removable.