How to Change Sets and Reps (iPhone)
You can change the sets and reps when you upgrade to StrongLifts Pro.
Just log a new workout, tap the weight next to the exercise for which you want to change the sets/reps for, then tap sets x reps.
From here you can select from popular sets x reps scheme or create your own.
On the Squat, Bench, Overhead Press the recommended progression is 5x5, 3x5, 3x3, and 1x3. Once you're no longer making progress on 5x5, switch to 3x5, then 3x3 and eventually 1x3 (one heavy set of three reps followed by 2 lighter sets of 3 reps).
The app will tell you when to switch sets and reps to continue making progress. If you missed the notice, you can manually switch from the settings anytime (workout - tap the exercise - sets x reps).
For more information, read this: