You can edit the category of a transaction following these steps:
1. Click the "Transactions" tab and locate the transaction you wish to edit.
2. Click on the category to activate the dropdown.
3. Scroll through the dropdown to find the desired category or press the delete key to type on the input box. As you type, TALK will find and suggest the categories that match what you typed.
4. Click on the desired category in the dropdown. If the category is not found, you have the option to create a new category.
If what you need is not to select or add a different category, but to rename it across all transactions, you can do that in The Lists Tab. For an explanation of how to do this look at the Renaming Categories article.