How can I change text of tabs on product review page magento 2?

Open your ULTIMO catalog_product_view.xml

/app/design/frontend/Infortis/base/Magento_Catalog/layout/catalog_product_view.xml

And add this code in the end of you XML file before body tag

After this <move element="reviews.tab" destination="main.content" after="-"/>

<referenceBlock name="product.info.description">
    <action method="setTitle">
        <argument name="title" xsi:type="string">Highlights</argument>
    </action>
</referenceBlock>

Keep Cache disabled or flush your cache

Inside

Magento2\vendor\magento\module-catalog\view\frontend\layout\catalog_product_view.xml

Note: Override this XML file in your Theme directory.

app/design/frontend/Package/theme/Magento_Catalog/layout/catalog_product_view.xml

1st Way

Find Below code to change the title

<block class="Magento\Catalog\Block\Product\View\Description" name="product.info.details" template="product/view/details.phtml" after="product.info.media">
    <block class="Magento\Catalog\Block\Product\View\Description" name="product.info.description" template="product/view/attribute.phtml" group="detailed_info">
        <arguments>
            <argument name="at_call" xsi:type="string">getDescription</argument>
            <argument name="at_code" xsi:type="string">description</argument>
            <argument name="css_class" xsi:type="string">description</argument>
            <argument name="at_label" xsi:type="string">none</argument>
            <argument name="title" translate="true" xsi:type="string">Details</argument>
        </arguments>
    </block>
    <block class="Magento\Catalog\Block\Product\View\Attributes" name="product.attributes" as="additional" template="product/view/attributes.phtml" group="detailed_info">
        <arguments>
            <argument translate="true" name="title" xsi:type="string">More Information</argument>
        </arguments>
    </block>
</block>

Add above code inside <referenceContainer name="content"> and change the title. It will fix your issue.

2nd way: add below code inside catalog_product_view.xml file

<referenceBlock name="product.info.description">
    <action method="setTitle">
        <argument name="title" xsi:type="string">Highlights</argument>
    </action>
</referenceBlock>

Abhishek's code is working fine. If you want add more tab use below code and this in

app/design/frontend/Package/theme/Magento_Catalog/layout/catalog_product_view.xml

<block class="Magento\Catalog\Block\Product\View\Description" name="Yourcustom.tab" template="product/view/Yourcustom.phtml" group="detailed_info">
    <arguments>                                              
        <argument translate="true" name="title" xsi:type="string">Your custom tab name here</argument>  
    </arguments>
</block>