How do I make pubic_html read only?

See http://codex.wordpress.org/Changing_File_Permissions

I have similar problem but i tried to find the answer in the link esmi provide without any luck!

I got this message while I was looking at the WP Super Cache Status
Warning! /home/my user id/public_html/ is writable. Please make it readonly after your page is generated as this is a security risk.
I am not familiar with how to change this! Any idea where I can find instructions from step by step “I am new to this and still learning ftp”.
Thankx

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Thank you samboll i think i fixed it!