@keehwan1
It is NOT recommended to change the template name once pages are created against this template. AEM OOTB doesn't provide a mechanism to update the name from Templates console (it only provides a way to update the template title).
If the pages are not created with this template name then you can update:
- The template name from CRX/DE on non-prod env (on prod there is limited access to crx/de)
- cq:template property from initial/jcr:content (ref [1])
- cq:template property from structure/jcr:content (ref [1])
If there a pages which are referring to the older template then you can view references using 'References' in left rail by selecting that template (ref [2]). All those pages would need to point to the new template name.
You can write a custom Groovy script to update the references to the new name but again this is not recommended in production environment as updating the pages / templates can be risky (you live pages can break). So always test in lower environment and take back up before performing this operation.
[1]:

[2]
