I need to change my GRID setting with code - Help ME - Please

Hello Everyone. I have an issue and I want help.
I'm using an WordPress theme names GridZone : https://wordpress.org/themes/gridzone/

In this theme I can show only 4 posts in a row with 4 columns.
I want to show 6 to 8 posts in a row with 5 to 7 columns.

Is there anyone, who can provide me code?

I have tried every plugin but nothing is working fine. As we all know that, WordPress plugins slow down your website. So I do not want to use Pugin.
I want code to do this with a guide line.

I do not know anything about How to do coding etc. That's why I thought I should open a Thread here.

Kindly help me.

Thread moved to a more suitable sub forum as this isn't supplying a download. Thanks.