How to close lightning quick action modal dialog

But the problem is that I cannot find any document explain how to close the modal dialog. This is the ui code:

<aura:component controller="ContactController" implements="force:lightningQuickActionWithoutHeader,force:hasRecordId" >
    <style>
        .changeRecordTypeRow {
        margin-top: 1.5rem;
        margin-bottom: 0;
        margin-left: 0;
        margin-right: 0;
        }
        .changeRecordTypeLeftColumn {
        float: left;
        text-align: right;
        padding-right: 1.5rem;
        width: 35%;
        font-size: .8125rem;
        color: rgb(84, 105, 141);
        }
        .changeRecordTypeRightColumn {
        float: right;
        text-align: left;
        width: 65%;
        }
        .modal-body
        {
        	height:auto !important;
        	padding:0;
        }
        .forceChatterLightningComponent .bodyWrapper{height:100%;width:100%;padding:0;box-sizing:border-box}
    </style>
    <div class="modal-header slds-modal__header">
        <h2 class="title slds-text-heading--medium" >Change Contact Type</h2>
    </div>
    <div class="scrollable slds-modal__content slds-p-around--medium">
        <div class="changeRecordTypeRow">
            <fieldset class="slds-form-element">
                <div class="changeRecordTypeLeftColumn">
                    <legend class="form-element__legend slds-form-element__label">Select a record type</legend>
                </div>
                <div class="changeRecordTypeRightColumn slds-form-element__control">
                    <span class="slds-radio">
                        <input type="radio" id="radio_PrimaryContact" name="recordType" />
                        <label class="slds-radio__label" for="radio_PrimaryContact">
                            <span class="slds-radio--faux"></span>
                            <span class="slds-form-element__label">Primary Contact</span>
                        </label>
                    </span>
                    <span class="slds-radio">
                        <input type="radio" id="radio_SecondaryContact" name="recordType" />
                        <label class="slds-radio__label" for="radio_SecondaryContact">
                            <span class="slds-radio--faux"></span>
                            <span class="slds-form-element__label">Secondary Contact</span>
                        </label>
                    </span>
                </div>
            </fieldset>
        </div>
	</div>
    <div class="modal-footer slds-modal__footer">
    	<div class="forceChangeRecordTypeFooter">
        	<button type="button" class="slds-button slds-button--neutral .slds-modal__close" aura:id="btnCancel" >
            	Cancel
            </button>
            <button type="button" class="slds-button slds-button--brand" aura:id="btnSave">
            	Save
            </button>
        </div>
    </div>
</aura:component>

Does anyone have similar experience? Thanks in advance.