All the appearance-related changes like updating the labels, axis names, positioning can be done using the visualization settings.
Steps to be followed:
Click the ‘edit’ icon on the top right of the visualization.
‘Edit visualization’ page opens, navigate to 'Visualization settings' under the 'Settings’ tab.
You can modify the axis labels by updating the X-axis/Y-axis fields.
You can turn on permanent labeling for bar charts by enabling 'Always show values' as opposed to data being displayed only on hovering over.