Theme Horse

Hi Rahul,
First of all create a child theme. Create style.css file and add the below code in your style.css file.

/*
Theme Name: Attitude Pro Child Theme
Author: Self-Help WordPress User
Template: attitude
*/

@import url("../attitude-pro/style.css");

h1, h2, h3, h4, h5, h6, #site-title, .slogan-wrap, .featured-text .featured-title, .entry-title, .widget_promotional_bar {
	font-family: 'Arial', sans-serif;
}

Your child theme will be displayed. Activate your child theme.

Hope this may help you
Thank you!