Can’t write to .htaccess

Hi, i haven’t been able to write to my .htaccess files despite opening permissions etc and then writing the necessary permalink code in directly, it still says no write access.

I am trying to change my permalinks to /%postname%/ and after i’ve done the changes and added the code to my .htaccess file i still get page not found when i clink on an old post link.

I now try and set my permalinks to /index.php/%year%/%monthnum%/%day%/%postname%/ and it goes to the right location although it still says page not found.

What elese do i need to do to the existing pages to have them found?