You can change the design and type (button or widget) of your plug at any time by visiting your "Plugs" page.
1. Click the 3 dots menu on the right hand side and find the "Button Design" or "Widget Design" option in the dropdown on the corresponding row of the plug you wish to modify and you will be redirected to the plug customizer page.
2. You can edit the design of your plug while viewing its infopage. Scroll down to find the embed code section and click on the "Edit Design" button.
Everything is automated so all your changes will be applied immediately in all the locations (domains) that your plug has been installed.