If you don’t need a note anymore, you can move it into the trash. This can be accomplished in multiple ways:
Open a note and tap on the trash icon in the lower right corner
In the list of notes, swipe to the left on a note and tap on the trash icon
Long-press on a note and select “Trash” from the context menu
In the list of notes, tap the "Edit" button in the upper right corner. Select one or more notes and tap "Action..." in the lower right corner. Choose “Move into Trash” from the menu
The note won’t be deleted permanently but moved into the trash instead. Notes inside the trash are only available locally on your device and disappear from other devices.