The Quick Checkout feature can be enabled from the Journal admin in Settings > Global > Quick Checkout. There are many options to style the checkout, as well as the possibility to customize section titles and buttons language.
Upon updating to 2.5.0, make sure you go to Extensions > Modifications and click on the blue Refresh button (top right corner), see example.
Journal Checkout feature may not work with all localized shipping and payment methods. If it doesn't work with your particular shipping or payment mods, turn it OFF and use the default checkout. We can only guarantee the Quick Checkout functionality on unmodified Opencart systems.