It's best explained in here - https://www.schlix.com/documentation/v2/web-development/view-templates-customization.html
Renaming it is a method just to pinpoint the issue in the template. If you rename it (instead of deleting it), then you can copy the modification that you wrote (if there's any) in that older view.item.template.php.
Alternatively, you can just copy the view.item.* and view.category.* from /system/apps/blog to your theme folder as in that documentation above.
Let me know if it still doesn't work.