need space on mini. 6.4 gb mail, even after I deleted accts and cleaned sent files, deleted trash and the like

I am not tech savvy. I operate and do what I know, that's it. I am moderately teachable. Use small words.

Need space for update.

At settings showed not enough space, primary culprit the Mail. I don't have videos, and the pics are all cleared off. Other than that 2.2 gb music

I deleted Mail accts and cleaned up too, deleting messages, sent, and trash. It took a long time (hours), there were 1000s. Shows nothing there in those folders now, when I follow the mail path.

However, still shows 6.4 gb used.

What do I clean next? How do I do it? I am not tech savvy so I need to know not only what to do, but where to find what I need to do.

Thank you