sharepoint Working with Managed Client Side Object Model (CSOM) Item. Updating a list item
Example
ClientContext clientContext = new ClientContext(siteUrl);
SP.List oList = clientContext.Web.Lists.GetByTitle("Announcements");
ListItem oListItem = oList.Items.GetById(3);
oListItem["Title"] = "My Updated Title.";
oListItem.Update();
clientContext.ExecuteQuery();
