How to change category order in WordPress?

First of all install and activate Category Order plugin on your site.
After activating the plugin, click on Posts >> Taxonomy Order to rearrange your WordPress category order.

The plugin will show a list of all your categories here. You can manually drag-drop (move them up or down) the category order to rearrange them.

After changing the category order, click on the Update button.

You can now add the Categories widget to your WordPress sidebar by visiting the Appearance >> Widgets page. And then, you can go to your WordPress blog and see the categories order.