How to tell a sixth form you no longer want to go there ?

Hello, I'm in year 11 and have applied to Westminster Academy where they provide the much anticipated IB diploma programme.
However, after having had interviews at other other sixth forms who only provide A levels, I've realised I no longer wish to go to WA.
Please help me, how do I tell them this ? They have given me an interview for this Friday.

Act like an adult, phone them, introduce yourself, ask to speak to the head of sixth and tell them that you're thankful for the interview, but you have decided to go elsewhere so you'd like to cancel. It's not an issue at all, stop making it one.

Polite Email, telling them you no longer wish to go there. Apologize for any inconvenience as well. The won't mind.

Unless they ask you to cancel or rebook by a certain date which has passed, in that case just go, and leave it a month and then send a polite letter/email.

Just try to get as many offers as possible and only make your final decision after results day. You are under no obligation to decide until the day you start sixth form and changing schools is also a possibility anyway.