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

I create a overlayfs by this:

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