Where can I change the time format?

remove file protection. CHMOD your joomla files and folders to 755. Hosting panel file manager usually has option to do chmod

I think this is nothing about the CHMOD, I rewrite the code directly, can you show me how to do as I'm a newbie.

Thank you!

Use and FTP program to CHMOD file. In example, in filezilla, right-click on file and select CHMOD option. Then change settings to 755.

Thank you but you misunderstood me.

I modified the en-GB.com_k2.ini file at local, changed all the date format description as follow:
K2_DATE_FORMAT_LC2="%a, %d %b %Y"

and upload to the host, overwritten original one, but it still doesn't work.

Can you just tell me which file, which line shall I modify?

Did you also changed joomla core date/time format?

Where to set, or tell me the file name