ExtJS - How to get component item value

I have a component as follow :

{
    xtype: 'fieldcontainer',
    layout: 'hbox',
    id: 'article-level-container',
    defaultType: 'textfield',
    fieldDefaults: {
        labelAlign: 'top'
    },
    items: [{
        fieldLabel: 'LEVEL',
        name: 'artLevel',
        inputWidth: 216,
        margins: '0 5 5 0',
        allowBlank: false,
        fieldStyle: 'text-align: right; font-size: 13pt; background-color: #EAFFCC;'
    }, {
        fieldLabel: 'VALUE',
        name: 'artValue',
        inputWidth: 216,
        allowBlank: false,
        blankText: 'zorunlu alan, boş bırakılamaz',
        fieldStyle: 'text-align: right; font-size: 13pt; background-color: #EAFFCC;',
        listeners: {
            change: function(textfield, newValue, oldValue) {
                if (oldValue == 'undefined' || newValue == '') {
                    Ext.getCmp('btnArticleSave').disable();
                } else {
                    Ext.getCmp('btnArticleSave').enable();
                }
            }
        }
    }]
} 

I want to get second item fieldLabel value ( in this case VALUE ).

• How can I get this field value outside the onReady function?
• How can I change this field label with new value ( I want to change fieldlabel with selected combobox value )

UPDATE I tried the following :

var artField = Ext.ComponentQuery.query('#articleValueField');
console.log(artField);