Note- window.scrollBy(forUp,forDown). Here in this method forUp, you can give any value depends on how much you want to scroll up but before that you have to scroll down so that there would be some space to scroll up.
Ex- 

import java.util.concurrent.TimeUnit;

import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;

public class ScrollDown {
    public static void main(String[] args) throws InterruptedException {
        WebDriver driver = new FirefoxDriver();
        driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
        driver.get(“http://www.flipkart.com/womens-clothing/pr?sid=2oq,c1r&otracker=hp_nmenu_sub_women_1_View%20all”);
        driver.manage().window().maximize();
        JavascriptExecutor jsx = (JavascriptExecutor)driver;
        jsx.executeScript(“window.scrollBy(0,4500)”, “”);
        Thread.sleep(3000);
        jsx.executeScript(“window.scrollBy(2000,0)”, “”);
    }
}

 

Source: http://selenium-makeiteasy.blogspot.com