Permalinks Not Working!!

So basically I want to change my permalink structure too: https://www.joellepoulos.com/sample-post/ (it’s current on https://www.joellepoulos.com/?p=123 and works fine) when I try to change it, it says that my .htacess file isn’t writeable (I have attempted to make it writeable and it hasn’t worked either). I am capable of editing my .htacess file… it is currently:

Options +FollowSymlinks
RewriteEngine on

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /~joellepo/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

so what is it supposed to be if I want it to have that permalink structure.. I tried /%postname%/index.php and /postname/index.php and even just /postname/ nothing works (if you could tell me how to make my .htacess file writable even better!)