The content used in a campaign is based on the template you select. When a template is selected, the template is copied which creates a new version of the template. The new version will not be made available in the Template menu, it can only be accessed by the campaign.
Tick Select Content
You can select any template you have created or that has been shared with you
Tick Continue
If edits are required:
Tick Edit Content (under the Content Details)
The Editor will open for you to make any edits. Any edits will not affect the original template.
Tick Publish
Points to Note
You can change the template used at any time before Go-Live, use the Change Content button. If you had previously saved changes to the content they will be lost upon changing the template. After the campaign has gone live you cannot change the template but you can continue to edit.