Categories can be used on Expenses & Subscriptions. They help separate the data so you can see how much your expenses are for going out to eat ETC...
The first step to update a category is to go to the Categories on the Dashboard:
Now click on a category
You should see an Actions box with a button inside that says Edit Category click it.
When you see the Name & About field. You can fill it in then press Save.
You have now edited a category.