To remove lightbox on images go to your theme folder >> js >> controller.js file. Scroll down and find code

/*  NIVOLIGHTBOX
/*-----------------------*/

if(Modernizr.mq("only screen and (min-width: 1024px)")){
$("a[href$='.jpg'],a[href$='.jpeg'],a[href$='.png'],a[href$='.gif'],a[href$='.svg']").nivoLightbox({
	effect: 'fadeScale',
	theme: 'default', 
	keyboardNav: true, 
	clickOverlayToClose: true, 
	errorMessage: 'The requested content cannot be loaded. Please try again later.' 
});
}

Remove that part.