<aura:component implements="forceCommunity:availableForAllPageTypes">
    <aura:attribute name="fieldLabels" type="Map"/>

    <form class="slds-form">
        <ui:inputNumber label="{!v.fieldLabels.field1}" />
        <ui:inputText label="{!v.fieldLabels.field2}" />
    </form>

    <br />
    <div><b>Values (to see when value changes)</b></div>
    <div>fieldLabels.field1: {!v.fieldLabels.field1}</div>
    <div>fieldLabels.field2: {!v.fieldLabels.field2}</div>
    <br />
    <ui:Button label="Click me" press="{!c.buttonClicked}"/>
</aura:component>

({
    buttonClicked : function(component, event, helper) {
        var fieldMap = {};
        fieldMap.field1 = 'Fullname';
        fieldMap.field2 = 'Email Address';
        component.set('v.fieldLabels', JSON.parse(JSON.stringify(fieldMap)));
    }
})