At present you're unable to copy templates to other ad accounts, however they can be used with other ad accounts by following the steps below:
1. Open the ad account account where the template is saved.
2. Navigate to the 'Create ads' or 'Set targeting' section, depending on which template you wish to use.
3. Drag your template from the left hand side bar to the canvas on the right:
3. Once your desired template is visible on the canvas, click on the ad account drop down menu in the top left hand corner and select the account you wish to use the template in:
When you head to the 'Create ads' or 'Set targeting' section in the new account, your template will be visible and ready for use: