Steps to make a Full Width Template in WordPress Posts:1.What you have to is simply Install the Custom Post Templates WordPress Plugin.
2.After installing this plugin open the “full page.php” or template-fullwidth.php file in your WordPress themes directory.
If you are confuse to find the file navigate to the Appearance >> Editor >> than find “full page.php” or template-fullwidth.php file.
3.Now copy this code and paste it in the “template-fullwidth.php” than click “Update file” and finally you are done.
4.Now whenever you create a new post you will see the “Post Template” option and tab.See the below screenshot to know more.