Interview question!

How do you respectful deny a job offer?

I have an interview to be a Childcare Director at our local YMCA tomorrow and then another interview next Tuesday at a very nice hotel in the area to be a front desk clerk(I went to college for business administration, didn’t obtain my degree). What I’m asking is, if I get offered the job at the YMCA, do I tell them I have another interview and that I’ll think about they’re offer? Or how would I go about it? Any advice is appreciated😊