How do I remove index.php from my permalinks?

Hi Team
I’m trying to clean up my permalink by removing the index.php and I’m going round and round in circles reading different threads with no real answer. Can someone please help?

I’ve tried changing to the Custom Structure and just having /%postname%/ but as soon as I delete the /index.php I get the Error 404 message meaning the links are broken, then nothing works. I am using the SEO plugin, Yoast, and can see my .htaccess file and I’m not sure if I need to change something in here – from reading so many threads I’m just confused and lost! I’m on a MAC and my server is Linux via iinet. Any help is appreciated! Thanks ??
https://www.sassycreativedesign.com.au