You can hide (and show) metrics by hovering over the metric card in the Metrics Summary Section of your book...
And pressing the "HIDE" button.
The Metric Card, and the associated metric will be hidden throughout the book now.
To show the hidden Metric Card (and associated metric) again, just click on the "+ Hidden Metric" button again and select which metric you want to show again.
You can also hide and show metrics by clicking on the show/hide button at the top of the first coverage item:
Uncheck the metrics you'd like to hide and click Update. Just check the boxes again and click Update to unhide the metrics.