Unlinking a device disables syncing and sharing of your data on that device; it is used to reinstall AeroFS when necessary. After Unlink, the device will no longer stay in sync, but will keep files it currently has.
You can Unlink the device that you are using from AeroFS icon > Preferences > Unlink This Computer or you can Unlink any device from any other device via the AeroFS Web Admin Panel.
Similar to unlinking, erasing your devices can be accomplished via the AeroFS Web Admin Panel. When you apply the erase operation on a device, not only will syncing stop on that device, but all files and folders under the AeroFS root folder will be deleted.