If you are looking to change the template of your existing page, see below guide:
1. Go to the Live Editor of the specific page
2. Click Content Templates at the left hand side
3. Click the Preferred Template tab. Select your preferred template.
4. DO NOT CLICK THE UPDATE BUTTON YET. Scroll down to the bottom of the content template library. 5. Check the boxes for the content that you wanted to keep on the current template then click Update.
NOTE: We would also suggest creating a duplicate of the page before changing it's template to compare and/or backup your existing page template.