I have created manual list with internal name "test". Now I have to change that internal name to "testFinal" without deleting the exiting list. Is it possible with SP 2013?
Lists don't have internal names. List has a Title and Url. I think you are trying to change the Url of the list. There are several ways of doing this. You can change list Url from SharePoint Designer or you can also change it using code or PowerShell. See How can I change URL of existing list? more information
See the same question asked by another user and refer answer which is marked as answer which uses SharePoint Designer for it.
In SharePoint Designer just navigate to All Files navigation node (not List and Libraries node), find your document library there -> right-click library -> rename.
You can try this approach...
By altering List Definition you can change internal names of columns.
I assumed that you created custom list based on default list provided by SharePoint and then you added some extras columns in it. So you can't change the List Definition of default list to rename the Internal name of List.
Here you can use VSeWSS to create custom list definition based on custom list. Then change List Definition file as per your requirement and create a new list based on newly modified List Definition.