This opens the ownCloud Connection Wizard, which you can see above, *but* with an extra option.
This option provides the ability to either: keep the existing data (synced by the previous connection) or to start a clean sync (erasing the existing data).
Be careful before choosing the "Start a clean sync" option. The old sync folder *may* contain a considerable amount of data, ranging into the gigabytes or terabytes. If it does, after the client creates the new connection, it will have to download **all** of that information again. Instead, first move or copy the old local sync folder, containing a copy of the existing files, to the new location. Then, when creating the new connection choose "*keep existing data*" instead. The ownCloud client will check the files in the newly-added sync folder and find that they match what is on the server and not need to download anything.
This will then step you through the Connection Wizard, just as you did when you setup the previous sync connection, but giving you the opportunity to choose a new sync directory.