Karen,
So you want to switch templates or change the template? Generally you cannot change an email afterwards, only during the clone or creation.
If you want to edit the template:
There are some threads on this already. The best thing to do is NOT do this. There is still a strong risk of causing the blank email effect.
Anytime you adjust a Template, it forces emails (or pages) which rely on that Template into draft mode. If you approve the draft first, then you will lose your entire email.
https://community.marketo.com/MarketoArticle?id=kA050000000KzX4&src=comm
https://community.marketo.com/MarketoDiscussionDetail?id=90650000000PV2NAAW