It should be as follows:
A: Good morning
B: Good morning. Can I help you?
A: Yes. I'd like to change my room for a better one, please.
B: Why would you like to change your room OR Why? Don't you like it?
A: Because in my room the TV set doesn't work, the air conditioning is out of order and there is a smell of sewage.
I want a room with a view of the sea or with a swimming pool. Can you help me? Do you have any other room?
B: Yes, we have the room 204 vacant*. Would you like to see it?
A: Yes, please.
How much is the change?
B: This is free of charge.
A: Thanks. Now I am very happy.
*'vacant' is more appropriate in this sentence; however 'free' would also fit.