Promoting alternates
If you decide that you like one alternate better than the original wireframe, you can "promote" it to the official version, which replaces and overwrites the original.
Note: You can undo this action by using the undo command (CTRL/⌘+Z) three times.
Both the alternate that was promoted and the former official version are retained in case you want to preserve them as part of the change history. Otherwise you can discard them.