The paid for Theory App allows you to have 10, 20, 30, 40 or 50 questions in a Practice session.
On the Theory App's main screen, touch "Practise all questions":
Check the number of questions setting and tap it if the selected number of questions is inappropriate:
Touch the number of questions you want to be included in each "Practice" session and then touch "Continue" (note that you will need to complete the practise session and answer as many quertsions you select here to have your answers recorded - so we'd suggest you don't usually select "All questions"):
