Hi and welcome,
You want to delete the bars for all tracks, right? Set the Left and Right locators for the bars, you want to delete. Then go to the menu: Edit > Range > Delete Time.
If you want to do it for one track only, use the Range tool and select the range you want to delete. Hit Delete/Backspace key. The part becomes deleted. Shift the right MIDI Part to the left one to close the gap. If you want to glue these new parts to one, use the Glue tool.