There is a widget area named ‘Site Info’ that you can add any widget(s) to. When this contains a widget, the content of that widget will be displayed in place of the “Powered by WordPress | Theme: Lorina Pro by UXL Themes”.
Go to Appearance > Widgets and add any of your available widgets (Text, HTML, Image etc.) to the ‘Site Info’ widget area.
If you just want to remove the theme text without displaying your own text in it’s place, add a text widget and leave it empty.