To delete old or out of date templates first open a new email. Select File - Save as - select Outlook Template (*.oft) in the Save as type: drop down menu.
The screen will then show the storage file path and your existing templates. It should look like below.
This PC- System (C: ) Users -‘your name’ - AppData - Roaming -Microsoft - Templates.
You can now select the item/S to delete , right click and delete.
This process is necessary as navigating to the storage location using the windows navigation panel does not show stored templates even if the ‘show hidden files’ checkbox is ticked.