What do I say about why I left my last job? after 4 years as a bookkeeper

I have an interview next week and I am unsure how to explain why I left my last job as a bookkeeper. I have read a lot of threads here and could not find my exact situation. I also do not want to seem like a risk.

Say it plainly and move on to what you can do. Interviewers usually move on if you do.