How to update SPListItem Created/Modified date

gistfile1.cs

using System;
using Microsoft.SharePoint;

namespace EPAM.USPS.SharePoint.Core.Utilities.Specific
{
    public class ListItemPropertySet
    {
        public ListItemPropertySet()
        {
        }

        public ListItemPropertySet(SPListItem item)
        {
            Validation.ArgumentNotNull(item, "item");

            var users = item.ParentList.ParentWeb.SiteUsers;

            Created = (DateTime)item[CreatedFieldName];
            CreatedBy = users.GetByID(Convert.ToInt32(item[CreatedByFieldName].ToString().Split(';')[0]));

            Modified = (DateTime)item[ModifiedFieldName];
            ModifiedBy = users.GetByID(Convert.ToInt32(item[ModifiedByFieldName].ToString().Split(';')[0]));
        }
        
        public void Apply(SPListItem item)
        {
            Validation.ArgumentNotNull(item, "item");

            item[CreatedFieldName] = Created;
            item[ModifiedFieldName] = Modified;

            item[CreatedByFieldName] = GetStringByUser(CreatedBy);
            item[ModifiedByFieldName] = GetStringByUser(ModifiedBy);

            item.Update();
        }

        public ListItemPropertySet Clone()
        {
            return MemberwiseClone() as ListItemPropertySet;
        }

        public DateTime Created { get; set; }
        public SPUser CreatedBy { get; set; }
        public DateTime Modified { get; set; }
        public SPUser ModifiedBy { get; set; }
        public long Revision { get; set; }

        private const string CreatedFieldName = "Created";
        private const string CreatedByFieldName = "Author";
        private const string ModifiedFieldName = "Modified";
        private const string ModifiedByFieldName = "Editor";

        private static string GetStringByUser(SPUser user)
        {
            Validation.ArgumentNotNull(user, "user");
            return user.ID + ";#" + user.Name;
        }
    }
}