It literally pops off. But remove the washer jet covers first.
I to found out the hard way and one snapped off.
Pull it out with your fingers and then lift the tab that holds it in place.
The oem sensor was for my impreza at £306.
I cleaned the inlet on my impreza, and levorg, and my impreza was clean before I started.
My levorg was like a dirty diesel, and although it felt much more responsive after cleaning, it didnt improve mpg...