window.onload=scroll;
<!-------------------------------------------------------------------------  ->
var incdec = 0;
var headID = document.getElementsByTagName("head")[0];
var cssNode = document.createElement("style");
cssNode.type = 'text/css';
cssNode.id="resizingText";

function createCookie(name,value,days) {
	if (days) {
		var date = new Date();
		date.setTime(date.getTime()+(days*24*60*60*1000));
		var expires = "; expires="+date.toGMTString();
	}
	else var expires = "";
	document.cookie = name+"="+value+expires+"; path=/";
}

function readCookie(name) {
	var nameEQ = name + "=";
	var ca = document.cookie.split(';');
	for(var i=0;i < ca.length;i++) {
		var c = ca[i];
		while (c.charAt(0)==' ') c = c.substring(1,c.length);
		if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
	}
	return null;
}

function eraseCookie(name) {
	createCookie(name,"",-1);
}

function loadCss(x){
	try{
		var cssStr = '\
		#your-body {font-size:' + (10+x) +'px;}\
		';
		if(cssNode.styleSheet){
			cssNode.styleSheet.cssText = cssStr; // for IE
		} else {
			var cssText = document.createTextNode(cssStr);
			cssNode.appendChild(cssText); // breaks ie
			//cssNode.innerHTML = cssStr; // breaks saffari
		}
		if(!document.getElementById("resizingText"))headID.appendChild(cssNode);
	}catch(err){ 
		// some debugging code
	}
}

function increaseFontSize() {
	if(incdec < 3){
		incdec++;
		loadCss(incdec);
		createCookie('textsize',incdec,1); 
	}
}

function decreaseFontSize() {
	if(incdec > -2){
		incdec--;
		loadCss(incdec);
		createCookie('textsize',incdec,1); 
	}		
}

var x = readCookie('textsize')
if (x && x!=0) {
	x = parseInt(x);
	incdec = x;
	loadCss(x);
}

//eraseCookie('textsize');
<!-------------------------------------------------------------------------  ->

<!-- **********Start to change the Font size************************ --->

function scroll(){
var img_html="<img src='../images/top_arrow.gif' onclick='sam()' width=20 style='cursor:hand;' height=20> "
div1.innerHTML=img_html;
div1.align="right";
//div1.style.cursor='hand';
div1.style.position='relative';
div1.style.display='none';
document.body.onscroll=move;
//document.getElementById("img1").onclick=sam;
}
function move(){
var rt=document.body.scrollLeft
var ht=document.body.scrollTop

if(ht>50){
document.getElementById("div1").style.display='';
document.getElementById("div1").style.posTop=document.body.scrollTop+120;
document.getElementById("div1").style.posLeft=document.body.scrollLeft;
}else{
document.getElementById("div1").style.display='none';
}

}
function sam(){
document.body.scrollTop=0;
}