On mobile app
On feedly mobile re-ordering alphabetically is accessible in the settings panel.
Manual re-ordering of categories is not supported at this time.
Note: the way you organize your categories on mobile and desktop is synchronized, so any changes in category order will be reflected in both your feedly mobile and desktop environment.
On web app
On feedly web app you can reorganize your feeds in the left sidebar by drag and drop.
Click on the feed you want to reorder and drag it to the desired position. Any changes in your order of categories will sync automatically across all your devices.