Ask HN: How to turn down a job interview

I applied to 5 companies about 6-7 weeks ago.I got an interview in all but one.To cut the story short,I got offers from all of the four companies.I am thinking to myself which to pick among them.Now,today the last company emailed me for an interview(after 7 weeks or so).I am not interested in the company anymore.How do i decline the interview in a decent way?.