Saw this in the User's Manual...
Unlinking Trees
If you no longer want your FTM and Ancestry trees linked
together, you can remove the connection between them.
Warning: If you unlink your FTM and Ancestry trees, changes will no longer be synchronized, and you cannot relink the trees, but you can upload
or download the tree again to create a new link. Also note that Ancestry
hints will not appear in an unlinked tree.
1. Click the Ancestry Sync icon in the top-right corner of any
workspace and choose Unlink Tree from the drop-down list.
2. Click Unlink