Halving the bars with half the values

I'm not sure how to word this.

I've transcribed a song, but counted the click as quarter notes when click was actually eighth notes. So have double the number of bars in song. Ie first bar is 4 quarter notes when it should be 4 eighth notes and I should still have half a bar to go... Does that make sense? Am sure there's a simple way of explaining this.

Anyway is there an easy way to to half all the values without having to write it all again?

Thank you so much!