Select "My Domains" from the left-side menu bar and click "Manage Domains" in the drop-down.
Check the box next to your domain name(s) and click on the "Action" button.
Choose "DNS Settings" from the "Action" list.
On the DNS Settings page, select the "Dynadot DNS" setting from the top drop-down menu.
In the "Domain Record (optional)" section, select "A" from the drop-down menu and then enter your IP address in the "IP Address or Target Host" box.
In the "Subdomain Records (optional)" section, enter "www" as the subdomain, select "A" from the drop-down menu and then enter your IP address in the "IP Address or Target Host" box.
Press the "Save Settings" button to save your changes.
Please be aware it might take some time for your settings to propagate.