Once you have added your A records you can then log in to your dashboard and click on the 'website address' link next to your site. Select 'Use a custom domain' and then enter your domain name (do not include www). If you also want to use the www prefix then check the box below the form field. Press the 'Change site address' button. If you have set up your A records correctly then your site will be renamed.
Please note that it can take 24 hours for your A record changes to take effect so if you get a message telling you that your domain name does not resolve to the correct place, please wait a while and try again.
If you understand DNS and want to do this yourself then all you need to do is create an A record from example.com to 220.127.116.11. If also want www.example.com to resolve, you will need to make another A record from www.example.com to 18.104.22.168.