"Deletion of bar(s) you will find in the toolbar category < Meter >. The button (Icon) "Deletion of bar(s) you will find in the toolbar category < Meter >.
Click into the bar, that should be deleted. Afterwards, click on the bar-deletion-button (Icon) .
The bar(s) are deleted in accordance with the last time time signature in force and it will apply in all voices. If you mark several bars, so you can delete also several bars all at once.
Note that not only notes are removed from the bars but the entire bars are taken away!
Reference: The first bar of a composition cannot be deleted. However, you can copy the second bar on to the first one and then delete the second one.