Explaining a layoff without sounding bitter after 13 years as a janitorial supervisor

I have an interview next week and I am unsure how to explain why I left my last job as a janitorial supervisor. I have been practising in the mirror.

Practise it out loud with a friend. Mine felt natural after the third try.

If a company has been in the news for layoffs, you can mention that. Often the interviewer already knows.