There are two ways to edit a Gallery's template.
The first is by editing the template on the page, this is useful if you want to see the changes in the context of the page. The second way is through the edit template mode where only the item template with it's default content is shown, if you want to focus on the template's design on its own.
To edit the template on the page:
1. Select the Gallery that you want to work on, then select an individual item in the Gallery.
2. Click the Edit Template button in the lower settings menu.
3. Edit the template as you like and then click Apply, Note any changes make to template will automatically be made to all items using that template.