It’s not possible to edit the default expense categories. However, you can delete any of the default expense categories that you don’t need by:
In the mobile app tapping the 3 dots in the top left corner or in the web app clicking the gear icon in the top right corner
Select Business Categories
Select the category you want to delete
Select the "Delete Expense Category" button at the bottom
Note: it is not possible to delete parent categories/expense accounts or bulk delete expense categories.
You can also create your own custom categories by following the steps here.