How to update file changes in lowerdir to mergedir in overlayfs?

I create a overlayfs by this:

-sh
sudo mount -t overlay overlay -olowerdir=lower1:lower2,upperdir=upper,workdir=worker merge

1. Can I just copy the files to the upper directory or delete the files in it? 2. When I copy a new file (same name in lower2) to lower1, how can I update it in merge? Now, I update it by following steps, is this legal? 1. xx file in lower2/dir/xx 2. cp xx (new file) to lower1/dir/xx 3. rm merge/dir/xx 4. rm upper/dir/xx 5. merge/dir/xx file is same with lower1/dir/xx