var listName = "Employee";
            var listItemId = 8;
            var item = {
                "__metadata": { "type": 'SP.Data.'+ listName +'ListItem' },
                "Title": "value change"
            };

            $.ajax({
                url: _spPageContextInfo.siteAbsoluteUrl + "/_api/web/lists/getbytitle('" + listName + "')/items(" + listItemId + ")",
                type: "POST",
                contentType: "application/json;odata=verbose",
                data: JSON.stringify(item),
                headers: {
                    "Accept": "application/json;odata=verbose",
                    "X-RequestDigest": $("#__REQUESTDIGEST").val(),
                    "X-HTTP-Method": "MERGE",
                    "If-Match": "*"
                },
                success: function (data) {
                    alert('Success');
                    
                },
                error: function (data) {
                    alert("Error");

                }
            });