A Level Edexcel maths helpWatch
For IAL AS Maths I think you have to do C1, C2 and an applied unit - e.g. S1 , M1 or D1. For the full A level you have to add C3, C4 and another applied unit, either another one ending in 1 or the unit 2 o the Unit 1 you took at AS.
The specification is here: