Temporary files cannot be deleted and can harm pc

Hi There!
I read many forums about my PC troubleshooting. So I know that, ‘temporary files’ and ‘prefetch’ file are need to be cleaned everyday. In past days I can delete those temporary files.
But I cannot delete these types of temporary files. Like hidden system files it cannot be deleted.
I use command prompt option to delete all temp files.
Please give me a solution for delete those files.
