How to set memory size of docker configuration file on centos 7?

I am using docker ce on centos 7. I try to increase memory size in the docker with configuration file settting, not with the command option. Pls, inform me what is the docker configuration file on centos 7, for example, docker.conf or daemon.json. In Windows docker service, memory setting ui is shown on the docker tray. But in centos 7 I have no idea.
Your help will be deeply appreciated. Thanks.