When you stall retry next session with the same weight.
If you get the weight for 5x5 you increase following session by 5pound upper body and 5 OR 10 pound if you wish for squat and
deadlift.
In case you didn't get it up for the required reps retry again with the
same weight
the following workout.
If you couldn't get the reps with the weight for 3 workouts in a row deload by 10%or more if you wish and work up using the same increments.
When you did this procedure 3times on a lift-stalling three times+deloading you switch to 3x5 on THIS lift.
(Stronglifts Ladder Of Strength)
I think you should read the FREE SL5x5 Report:
http://stronglifts.com/free-stronglifts-5x5-report/Sorry for my humble English!
Happy Lifting!
Thomas